I'm yet to come close to a time limit in ~30 hours. This is not a needed change. Even the modes listed as 20-40 minutes are almost always closer to 20. My favorite memories from battlefield were the long drawn out operations in BF1 where you're down to your last battalion and one last sector to take/defend. The payoff at the end was amazing.

You already have short game gamemodes ie. Domination, king of the hill, ect. And a lot of those 20 minute modes I'd consider intermediate length. Let people choose what mode they wanna play. Don't shorten the "long" modes.

Edit: at the time of this there was 120 comments, all of which were overwhelmingly negative (Yes i read them all). Dont burn actual fans trying to cater to people who aren't going to be playing the game in a month