Presumably you’re going to rent the rest of your touring setup (skis, bindings, skins, etc). Why not also rent boots which are designed for what you’re doing?
Anyway I would have thought the smart thing to do would be to first try a half-day tour before committing to an overnight. That way, your feet have a few days to recover from the damage you inflict on them. (Actually even with a good-fitting pair of touring boots which I own, it’s not unusual to get a blister on the first day of the season).
And whatever kind of boot you try, if you find you didn’t like it, you can try something else before going on a multi-day trip.
Three hours for two days in a row skinning in downhill boots strikes me as fairly discouraging for any future ski touring.