The ONLY reason in favor of the time limit is because of the technical limitations, which doesn't really make sense since other games don't have that limitation AFAIK

For those who don't mind the timer, removing it wouldn't affect your enjoyment of the game at all. If you like the timer but always clear the dungeon before the timer is over? Congrats, removing the timer doesn't affect you at all.

What if you're running a dungeon through the duty finder, you researched the fights beforehand...and the other people in your group haven't? You try to teach them all the fights, and you wipe a couple times on each boss but you're making good progress. Then you get to the last boss and...time runs out. You lost 90 minutes of progress. ESPECIALLY when the main story REQUIRES dungeon running, that can be a real pain. In this instance, it's not even your fault you ran out of time! But, you still got shafted. I simply see no real reason to have a timer.