Auto-translated
I also play with Chaos magic and Rangers (and I use Letus as my main hero, who uses Plague at the beginning of the battle, which doubles the effect). My record in Hero mode is 125 days, and I defeat the main hero on day 41 (considering that, according to the scenario, he should appear only on day 35). After that, it becomes a monotonous grind (or rather, a grind against the outpost). Even in the most favorable scenario, when I managed to get a full set of Sar-Issa's attire, it's still impossible to summon more than 140 Priests and other units at once (about 25 Titans, 10-15 Dragons, etc.), which means you have to attack the outpost at least 10 times. This takes 40 days, even with the most upgraded logistics and Traveler's Boots. In this regard, I would believe someone if they said they completed it in 100 days, but 45 days is the limit. Maybe there are some tools I'm not aware of?
Oh, I completely forgot to mention that the garrison (as well as the enemy hero with significantly superior forces) is, of course, attacked by no more than 7 Rangers. You terrorize the garrison with Plague and Chaos until you have only one Ranger left (and then you retreat home).
By the way, in the online game, there is a great countermeasure against this: enchanted arrows of the High Elves kill invisible targets (and, of course, there is Armageddon, Word of Destruction, Mines, Wall of Fire, Meteor Shower, Plague – all these spells destroy both Rangers and Night Lords)