I will totally troll people if 3-4min system set became a thing for PvP TT lol. I mean, I get that some people can't think fast enough or feel pressured and panic a little (because I definitely do), but that's still a very VERY long time. You're looking at a minimum of 15-20min games if I were to do that LOL. This isn't chess. This is more akin to checkers for the amount of thought you need. 1 minute, however, seems perfectly fine and ideal to me (or the player set time limit). This is a math game. If you're horrible at math, you're probably not going to enjoy yourself very much regardless of time limit. I hate math, but I can certainly function basic addition, subtraction, and number matching just fine.
Against NPCs, time limit kind of makes sense, but feels unnecessary. They're probably afraid of hundreds of people simply AFKing while accessing the NPC. Might be for potential problems that arise in case of that. It's also likely to be partially because of PvP reasons, where they DON'T want players to have unlimited time (because of people like me that will just troll you if something ridiculous like that happened). At first, especially when you just started to challenge an NPC, you're gonna wish you had that extended time limit but the results are likely going to be the same at first. After a while though, it's systematic because you become familiar with the NPCs cards and how it plays them. Time limit means nothing after a while.
Honestly, the big picture of it is that TT is a training game (see Brain Age). You're intended to eventually think faster and more efficiently the more you play. You become more accustomed to the cards, rules, and your opponent(s), not to mention you're becoming better at problem solving, basic math, and working under pressure. At least, that's how it is CURRENTLY set up. Which is funny, given that by taking out the basic math function, this really isn't much different of a training process than learning a new dungeon/raid/boss/etc. If they ever change it, then that might not be the case, but for now, it is what it is.