Is it okay if i masturbate a few hours after receiving first dose of hpv vaccine ?

Yes: It will not interfere with the effectiveness of the vaccine.

Before and after...: Normal men, women, boys, and girls masturbate (it's universal). It is not harmful, as a body goes through similar effects during regular sex with a partner (but avoid going to extremes). If it was ok for a particular person to masturbate before a vaccination, then it should be ok to masturbate after that vaccination (maybe with the unvaccinated arm, if the plan is to "masturbate a few hours").