All things being equal, the player on defense in this game is in a stronger position than the player on offense. Simple but powerful utilts and dash dance grabs allow an alert opponent to punish most attempts to approach. To compensate for this, players will space camp with effective aerials and dash dancing mind games, all the while waiting for their opponent to screw up and leave an opening. This can result in a slow moving match, even on a stage like Dreamland. It also results in matches that aren't terribly fun for others to watch.
The real problem comes up on a stage like Hyrule. A very common situation on this stage is to have one player on the central platform and the other player either in the pit or on the slope on the left side. Neither player wants to approach the other here because doing so requires committing to a movement pattern that overcomes the change in elevation. This reduces options for the aggressive player, which makes that player easier to read, which makes that player even easier to punish than usual for the defensive player. This situation happened multiple times with Boom vs Isai at Genesis, and probably happened a bunch with Sensei vs Kefit at Apex too.
So why is a situation like this eventually resolved in lieu of a time limit? Well, it's a combination of players not having infinite patience and of playing a 12 year old game because, god dammit, they love that game and want to actually play it. But these factors stop mattering in a competitive enough environment, when playing to win takes precedence over all else. While Apex 2012 wasn't quite at this level of competitiveness, it was close.
I think it's quite obvious that a time limit, when added to a competitive environment like this, will lead to massive stalling and camping on Hyrule, and potentially on other stages. It would actually validate the strategy of getting a stock advantage and then running away forever by triangle jumping around the pit or simply by going back and forth with quick attacks or Kirby's aerials or planking or whatever. I also don't think a "no excessive stalling" rule can co-exist with a time limit. A time limit exists because it's a clean easily adjudicated rule that resolves the main issue that a messy subjective anti-stalling rule would be meant to address - that is, it forces matches to end so that tournaments can carry forward at a reasonable clip.
I also don't think a "no excessive stalling" rule can co-exist with the sort of competitive environment that gives rise to the concerns expressed in this thread in the first place. It's simply too subjective and messy. What separates stalling from a valid but hyper careful and defensive strategy? We can try and pick out some easy examples, such as saying that a DK player must throw a grabbed player within x seconds of initiating the grab, but there's no way that rules like these can cover even a tiny shred of the stalling possibilities. Especially when other methods don't involve the use of moves/tactics as immediately dubious, identifiable, and intentional as DK's chain grabbing.
Man, that's a lot of talking about Hyule when we are supposed to be talking about time limits! Well, I don't think time limits will effect gameplay on the smaller stages all that much due to the infeasibility of stalling forever (though Kirby/Jiggly air camping and/or planking might prove me wrong). Yes, a good Fox can run away from a slower character all day on Dreamland, but it takes skill and thought on the Fox player's part. Eventually the Fox will **** up and die or will win. If matches last too long on smaller stages then that's probably just a problem with the way the game forces itself to be played - defensively. In this case the sensible solution is to lower the number of stocks.
But this doesn't fix Hyrule. I'm not sure anything can fix Hyrule. A time limit will have the opposite effect, and lower stock numbers won't defeat the issues inherent in the uneven positioning situations and subsequent camping/stalling provided by the stage. Don't give me wrong, I love playing on Hyrule and think it's a great stage in the absence of hyper-competitive play. But it probably can't survive in an environment focused excessively on winning above all else.
Unfortunately, removing Hyrule would have some drastic effects on character viability and would lead to even more Falcons in this world. But that might just be part of the growing pains this game needs to go through if we want to treat it in a more competitive manner.