And sometimes shorter! 25 minutes is very long for MAN - I hope their standards aren't slipping. Was this T3? Generally I find T1 security is the slowest.
I'll go along with that with regard to T1. As for T3, when ive been flying down to LHR on the early afternoon BA flight, ive turn up at security at it's virtually been empty.
To the OP, as already been said, plan to be in T3 for 6am and you'll be fine.