Hi just some thoughts from my side - as I had a smiliar case with them some years ago...
- Edelweiss do this systemtatically: lot of their flights are due to arrive shortly before ZRH airport closes down. If a plane gets stuck during the day for whatever reason they wait with the last flight so it can fly out just before ZRH closes and then return the next morning just when ZRH reopens again. Then the plane is there ready for its usual schedule. Fine for Edelweiss, really unpleasant for the the clients who have to take a return flight at 3am somehwere with Children as a nasty holidy suprise.
- if you apply for compensation they will rather quickly send you a letter denying your claim with wired reasoning and the case is closed. You will need to reply to this letter with the following -
- The will say that the Jurisprudence of the Europen Cour of Justice does not apply to them only the EU directive. [Difference is: EU directive only gives right the compensation if there is a cancellation - only the ECJ decided that a long delay is equivalent to a delay]. Thus remind them that your flight left from Spain which is EU and therefore the ECJ jursiprudence is applicable.
- The will tell you that rotation was the issue (for whatever reason) - you need to reply that:
a) The EJC judeget that a larger airline such as Edelweiss needs to have a reserve airplane at its Hub for exactly this reason, reason to fail to do does not excempt them
b) They do systematically do this (delay airplines on the last rotation of the day) because and therefore this cannot really be consdired as unforeseen circumstance and force majeure, but is a risk they willingly take and therefore they are liable to it.
Demand payement withing 30 the inform them that you will take them to court to court (you can then use one of the agencies). Also let them know that you file a claime with respective Spanish and Swiss authorities (Note that this will not be helpful to get compensation, it will just annoy Edelweiss/Lufthansa)
If this sounds too cumbersome just take one of the claim agencies straight.... but you need the chosse one that is willing to take Edelweiss to court in Spain (not in Zurich).
Hope this helps