HoMM3 HD bug reports.

What is meant by autosave?

- automatic saving that occurs at the end of a turn. (including daily saves)

Thus, it turns out that you can save with a name containing three digits (789, for example) and gain 10 minutes.

No. Any "manual" save is not an autosave. You could easily check this and be sure before writing.

Previously, in HD, when loading an autosave, the timer was set to the beginning of the day, as if you hadn't spent any time on that last turn, and after passing the turn, on the next day, the timer increased as usual. That is, if you spent 1.5 hours on a turn, when loading the autosave and passing the turn, you would get a bonus of 1.5 hours. And this is despite the fact that after the autosave, it's the opponent's turn, and you can sit and think about the game for the entire turn.
Now, when loading an autosave and passing the turn, you don't get any bonus at all. But from loading to passing, you and your opponent can sit and think for up to 10 minutes.
What is better, as it was or as it is now?
Are 10 minutes too much? I can make it even 1 second. Is it too little? - even a day.
I took 10 minutes completely randomly.

As a rule, the game is loaded more often after disconnections or just saves, and not autosaves.

So what? An autosave at the end of the day differs from a regular save in that you have already done everything you wanted in the turn (if, of course, the end of the day was not due to the timer running out), so any time bonus before passing the turn cannot be spent on the game itself.

Quick save with F6? What is it for in online mode?
Wouldn't it be more convenient to have autosaves before and after a battle?

And in the latest game, the timer ticks constantly. Even with the "After press Ok" option enabled.

What do you mean by "latest game"?
The value of the "After press Ok" option is set only at the start of the map. When loading, it is taken from the save. You can check if the option is enabled in the game through "scenario information" -> "more options".

In RC11, there was a serious bug, not in the implementation of the timer, but in memory corruption that miraculously affected the timer (it's good that it affected it and not some less noticeable place). It was fixed in RC20.

In RC27 (or maybe earlier), a bug appeared with the "Start timer after pressing Ok" option not working and the timer being added twice to the blue player in HotA. This was fixed in RC30.

There were no complaints about the timer in RC30, if there are really problems in RC30, then just write about it.

There is not much point in reporting bugs in the latest version. Reports like "in the latest version, this and that" are even more meaningless, because it's hard to figure out which "latest" version you have, especially since while you are writing or while I get to read it, HD may have been updated 100500 times. Mixing several versions in a report is also of no use.
You have a crash log from RC27 with a crash occurring during the start/loading/saving of a map in single-player mode, although, based on the meaning of your post, I expected to see a crash log when viewing a turn.