We were on a connection so ended up with 3 hours in T5. For our first time in F, we thought that this was about right to experience everything without being rushed. Obviously, the frequent flyers will want to spend as little time as possible in the terminal and but for a holiday, you'll want to idle your way through security, find a spot in the lounge, visit the spa, sample plenty of the food & drinks menus etc. You'll need to leave the lounge at least 45 mins before departure so it's pretty easy to fill up an enjoyable 3 hours and not be bored.