The time limit is a big part of it sure. But a lot more has to do with just the way everything is so complex and interwoven. If you make a bad choice it's not always immediately obvious; then it bites you in the ass 20-30 turns later and you are kind of just fucked, you don't really want to load a save that far back at that point.
The rapidly declining morale of your troops is also a huge issue, that gets harder to manage the more troops you have, since the easiest fix is talking to them and giving them a bonus but you can only do that with one character per turn. The Hawaii event and hot spring can help with this, but you get access to those way later in the game, unless you are willing to save scum for 20, 30 minutes, maybe an hour lol - to get a hawaii ticket from searching prisoners, reloading a save, search again, over and over until you get lucky and the RNG gods grant you a ticket lol.
The game also has (in typical Alicesoft fashion) a million things that trigger based on your actions, and are seemingly designed to be at the worst possible time. If you attack the wrong province at the wrong time, you can trigger the start of war with one of the factions you were not planning to fight yet. You also need to attack in a certain order to make it viable to get certain characters. Sometimes, you are waiting for an event to trigger and burning turns or not proceeding in the most strategic fashion, like when you capture the district with the rice cracker store, that part is such a bitch because you have to wait around for the scenes with two important characters to play out, or else you will not be able to capture them. (The rice cracker store owner and the woman that has a crush on him, I'm blanking on their names at the moment and don't feel like looking it up.) Then for extra fun, you have to get a bunch more events to trigger before you can recruit that woman out of the prison, and if you capture the lady in the wheelchair who makes tanks inaccurate BEFORE you have managed to recruit the woman who loves the cracker store guy, well you're up shit creek. So it's just a lot of events subtly chained together and you realllly need to know what the fuck you are doing to get things to come out the way you want them to.
Capturing characters can also prove really challenging when RNG just decides to fuck you in the ass. Can't tell you how many times I had to reload saves because I managed to bring a character I wanted down to very low health but they still escaped, OR I screwed up and accidentally did like 1 or 2 points more damage than I expected to and killed them by accident. OR my character died trying to do one of those merciful hits (this can happen easily with Sinae who is one of your only options if you need to do a merciful hit early on. You are kind of gambling on her hitting the enemy AND them not countering or their attack missing, because that early in the game her HP is likely not adequate to sustain a hit from a good enemy you want to capture.)
I actually love the dungeons, my biggest gripe was always feeling like I didn't have enough turns/actions or could not spare enough troops because I need so many on defense in border cities by mid to late game. In general the game would be way more fun to me if there wasn't quite so much pressure of endless hordes of enemy armies constantly at your doorstep on multiple fronts.