For hep b vaccination for 19 yr old for the 3rd dose (which he got early sept) is it ok to get in early march or should wait until exact after 6 month?

Wait: He needs to have the third dose at least 6 months after the first one - it can be longer than 6 months but no less than

Hepatitis B vaccine: The second dose should be at least 1 month from the first one and the third needs to be 6 months from the first one, From September to March is 6 months, so that should be fine.

Hep B #3: HepB-3 should be administered at least 8 weeks after HepB-2 and at least 16 weeks after HepB-1. Hope this helps.