Auto-translated
In 2 days, I counted 2 or 3 possible routes, and 2 more that seemed like false leads. The simplest route takes 2 days. On day 1, two heroes, Jelu and Kir, reach the Stronghold. On day 2, two heroes with a speed of 10, Lorelei and a Unicorn specialist, reach the green keymaster's tent. It seems the map was initially "designed" for a 2-day completion.
A simple way to complete it in 2 days.
Day 1: We break into the Pandor's Box, take the Stronghold. From the Stronghold, a hero with pass-fighting skill runs to the quest for the Grail of the Titans. A hero with a speed of 10 stands on the pond. We get the Behemoth using the machine gun.
Day 2: We visit the tent, collect the Grail of the Titans, and then, using the Bull and the Devourer, we get the Tome of Earth.
A more complex option with maximum parameters: We gather 2-3 Behemoths and defeat the rusty dragons (the Grail of the Titans doesn't work on cursed land). Then, we go to the Azure using the "walk on water" spell.
The options involving flight or the Utopian seem to take more than 2 days, but I didn't look at them in detail.