Any time that I had to prove something such as what you are discussing, the airlines actual arrival time or departure time of the flight is what was used for the relevant data point. Nothing else was considered to have mattered, as it was unverifiable.

But, as I am not a representative of your government's tax department, it's best to check with them. There are several travelers here in the European continent who may answer as well, if a mod moves this to the appropriate forum.