"War of the Strongest"

1. The question is this: I already completed it one way, but saved at the end of the day. Does that option no longer count?

It would be desirable to replay it… and thereby we will kill two birds with one stone.
Bird #1: You will improve your result (because in 99% of cases, replaying a map leads to a significant improvement in the quality of completion. i.e., if translated into Russian: by replaying the map again, you have a 99% chance of gaining more experience. And this gives you a chance to take a higher place in the final table.
Bird #2: You can save at the beginning of the days as well.
But, in principle, you don't have to replay it. It’s up to you. But if there is suspicion of cheating, then...

Can all necessary saving scenarios be described in one text?

Unfortunately, I didn't understand the question...
Could you explain your question more clearly?

2. The topic describes one day, if I'm not mistaken, but we have 27. Should everything be described? It will take someone more than one day to read :)

Hmm… I gave a not very good example.
Try looking at this topic and also this post and this one. Hopefully, the issue will be resolved. :)

Sincerely.