No, 5 days later is not "at the earliest available opportunity" if you were able to find an earlier alternative flight on another airline.
"At the earliest available opportunity" means precisely what it says. It does not mean "at the earliest available opportunity on one of our flights".
Regulatory authorities still try to balance the rights of the passengers and the burden on the airlines, so they they will accept it if, say, there was a flight on another airline 1 hour later but they put you on one of their flights 2 hours later. But 5 days later is definitely not "the earliest available opportunity". The cut-off is usually placed at "same day" (by case law).
There are a number of alternative options the airline must consider:
- Flights on the same route they operate, in the same class
- Ditto, in other classes, if applicable
- Re-routing via an intermediate point on flights they operate, if applicable
- Re-routing to alternate airports, if applicable
- Flights of partner airlines, if applicable
- Flights of any other airline
- Combinations of the above
While this is not set in stone in EU regulations, there's a very good interpretation by the UK CAA (based on EU regulations and case law which still apply for the UK in this situation): Re-routing in accordance with Article 8 of Regulation (EU) 261/2004 as retained (and amended in UK domestic law) under the European Union (Withdrawal) Act 2018 and the CAA’s view on compliance.
Here's their summary of one particular relevant case:
C-354/18 Rusu v SC Blue Air — Airline Management Solutions SRL
2.4 The case of Rusu v SC Blue Air confirms that Article 8 requires airlines to offer passengers the option of reimbursement or re-routing. It also states that airlines must provide comprehensive information to passengers about the re-routing options, including flights on other airlines, to allow them to make an informed choice. The Court also found that there was no obligation on the passenger to do their own research to find information on alternative flights. In addition, the Court found that airlines were responsible for offering and organising re-routing and had the burden of proving that the re-routing offered was at the earliest opportunity.
Here's their view of what an airline should do:
4.1 When identifying re-routing options under Article 8(1)(b), airlines will often be able to identify a number of potential re-routing options. The CAA’s view is that, in such cases, in order to avoid further disruption to the journey plans of affected passengers, when offering the choice between the three options10 under Article 8(1)(a), (b) and (c), airlines should always seek to offer the affected passengers the re-routing option under Article 8(1)(b) which re-routes the passengers on the same day as their original flight and via the same route. If this is impossible, airlines should seek to identify alternative re-routing options under Article 8(1)(b) which minimise the disruption to the journey plans of affected passengers.
4.2 The CAA accepts that, when offering the choice between the three options under Article 8(1)(a), (b) and (c), airlines will normally prefer to offer affected passengers a re-routing option on their own services or, where applicable, those of their partner airlines. In many cases, this will also be the best outcome for affected passengers. However, in circumstances where there is no re-routing option under Article 8(1)(b) on its own services or, where applicable, on the services of its partner airlines, on the same day as the original flight and via the same route, the CAA’s view is that the airline should next seek to identify re- routing options on the services of alternative airlines on the same day as the original flight and via the same route. If such a re-routing option is available, affected passengers should be offered the choice of this option at the same time as they are offered the choice between the options set out in Article 8(1)(a), (b) and (c).
4.3 In circumstances where there are no re-routing options under Article 8(1)(b) on its own services, or those of an alternative airline, on the same day as the original flight and via the same route, the CAA’s view is that the airline should next identify re-routing options available on the same day as the original flight but involving (a) the use of alternative airports located in close proximity to the original departure and/or arrival airports on both its own services and those of alternative airlines; (b) the use of alternative indirect flight routes on both its own services and those of alternative airlines; and (c) the use of alternative modes of transport. Given that such re-routing options are likely to lead to additional disruption to the journey plans of the affected passengers, airlines should seek to identify re-routing options which minimise this disruption. In cases where more than one such re-routing option is available, airlines may wish to allow affected passengers to choose between these re-routing options at the same time as they are offered the choice between the options set out in Article 8(1)(a), (b) and (c).
4.4 In circumstances where there are no re-routing options under Article 8(1)(b) on the same day as the original flight, the CAA’s view is that the airline should identify re-routing options both before and after the day of the original flight, both on its own services and those of other airlines and transport modes, and via the same route as the original flight as well as alternative routes. Given that such re- routing options are likely to lead to additional disruption to the journey plans of the affected passengers, airlines should seek to identify re-routing options which minimise this disruption. In cases where more than one such re-routing option is available, airlines may wish to allow affected passengers to choose between the re-routing options at the same time as they are offered the choice between the options set out in Article 8(1)(a), (b) and (c).
4.5 For the avoidance of doubt, the CAA does not consider that airlines are obliged to take manifestly unreasonable steps to re-route affected passengers, such as by offering transportation by private jet or private international taxi for long distance journeys.
(emphasis mine).
So, no, 5 days later is most definitely not "at the earliest available opportunity", and they failed to provide you the choice between the 3 options.
Further:
6.7 As described previously, and as clarified in Rusu v S C Blue, it is the CAA’s view that it is the responsibility of the airline to be proactive in identifying suitable re- routing options and contacting affected passengers to expressly offer them the choice of options required by Article 8(1).. In circumstances where the airline has failed to contact affected passengers in a reasonable period of time, these passengers may then be justified in making their own arrangements and seeking reimbursement for the cost of doing so, so long as, consistent with the principles set out in McDonagh v Ryanair Ltd, the expenses incurred by the passenger were necessary, appropriate and reasonable to make up for the shortcomings of the airline in offering the passenger a suitable re-routing option.
(emphasis mine)
Note that you should be careful not to ask for a refund (that "liberates" them from their obligations to you), but for payment of the alternative arrangements you had to make.
