Having a nasty suspicious mind, I always try to get to the airport a minimum of 2 hours beforehand. Doesn't always work, of course, but the aim generally allows for motorway problems. Not always - one Monday, I allowed 2-1/2 hours to get to Gatwick to arrive 2 hours early. I arrived at check in 20 minutes before departure. It so happened that my flight had been cancelled anyway!
What can be a problem at T5 is that you see the board announce 'go to gate', the gate is 10 or 11, and you're in the south lounge. By the time you get to gate, you're amongst the last to board, and on occasion, they;re even calling for you. That's less than FIVE minutes after it the 'go to gate' flashes up!
Bit of a lack of co-ordination somewhere there, I think.