I was a little annoyed in a Sunken Temple run yesterday
by the time we reached the second boss we only had 40 minutes left

long story short we didn't even beat the second boss.

that's when I realised that the timer at least meant I wouldn't be stubburn and stay in the instance as long as it would take. with that group we would have never made it.

so, while I do think the timer is a little silly on the '90 minutes for almost everything', in general I'm a fan. I just wish the timer would be more reasonable for the different dungeons.

in Stone Vigil for example, the first time I did it I watched all the cutscenes, we failed once on the first boss and twice on the last boss, and we had about 10-15 min left at the end.
that's hardly a lot of time for mistakes, and we had a pretty damn good tank that knew exactly how many mobs to pull, pull them around corners, explained all the boss mechanics in a pretty straight forward way.