I just finished a battle that lasted 7 hours, with 16 Archdevils against 1,000 Crystal Golems with relatively low stats. Without turbo animation, each stack took about 50 minutes, followed by 10 minutes of rest, totaling around 4-5,000 rounds. And there was practically no room for error, as 50 dragons were already one-shotting the Archdevils, and there were 140+ of them in each stack. However, this didn't prevent me from failing once when there were fewer dragons in the stack than needed for a one-shot, so I had to restart.
It would be extremely frustrating and unpleasant to misclick after several hours of battle and lose, so the ability to save during a battle would be very useful, although it would be quite similar to cheating. There are also conventional methods; you can run the game on a virtual machine and periodically create a snapshot during the battle. Or simply put the system to sleep during the battle, copy the hiberfil.sys file, and then use it before each wake-up. But all of this is quite inconvenient.
P.S.
I still had to replay that battle because I made a mistake in the strategy earlier