Herms are very rare and something you almost have to purposely work at to get them so stop worrying about them.

The length of time doesn't matter. You take cuttings when you have some to take.

If I were you I'd wait until sex shows naturally. Most strains show by the 5th to 6th week or when alternating branching is well underway. Flowering to determine sex only adds several more weeks to the veg period unless you're planning to flower as soon as sex shows...but if you do that you you'll have far less yield and fewer cuttings to start clones.