I don't know, I don't hire a second hero in the first week; I prefer to build Minotaurs instead. Because the main mines are important, and the main hero can capture them (is it really that hard to run to an extra tile?). The resources near the mines can wait until the next week; they won't disappear (I've tested it). And Minotaurs will be very helpful in the second week during battles with tougher neutrals, otherwise, there will be no one to protect the Fury units (and it's a pity for the Stalkers too). So, in my opinion, the best time to hire a sixth hero is at the beginning of the second week.
In the second week, the Fury units are protected either by Hydras or Raiders, and this is already breaking through defenses consisting of units of level 5-7, and even then, it's often possible to do it with just Stalkers (if the main hero is Leto). I build Minotaurs in the 4th week, if I have time.
Творят настолько черные дела,
Что до таких блистательных идей
Не вдруг дойдет и записной Злодей
Темный адепт клана GODS