Last week at Malaga I arrived 3 hours before departure to do some work in the lounge (flying CE). Was told check in won't open until two hours before the flight and in the end it opened 1:45 before the flight. Didn't have much time in three lounge at all.

Tomorrow I'm returning from Heathrow T5 in CE, what's the earliest I'll be able to check in there and access the lounge? I've read conflicting info, some says 3 hours, some 12.

thanks