Studies I've read (abstract at any rate) indicates 3-4 hours was not enough. They ended up doing 14 hours / day or so. Not sure if that is even doable in a tour, so much phaffing around with transfers, etc.
I don't think I saw any studies where they did 14 hrs/day for 2-3 weeks to boost Hgb then followed with 3-4hrs / day maintenance though, that'd be interesting.
Did you see that study where altitude training (LHTL) was found to increase testosterone production? I went looking after reading Aldo Sassi apparently saying that was one effect of altitude training to a journalist who was discussing Sky's altitude training camps (the same guy who said they don't care about Hgb increases).
Seemed really strange. Noone else mentions it - not even our resident PhD, Sky-loving residents.
It felt more likely to me that riders were using it to help with recovery when training at altitude and the researchers were just recording test levels, and not looking or able to differentiate exo from endo-genous.