If I'm looking at a listing for a seed and it says, "flowering 5-6 weeks". Does that mean that it flowers for a duration of 5 to 6 weeks or does it mean it flowers during week 5 and 6?
It probably means it flowers for that time period. Weed can be put into flower by switching to a 12/12 light cycle. Even young plants can be forced to flower but the flowering period should be pretty consistent among strains.