adjustement for a medication time.

I 'd like to know if there is any policy regarding the adjustement of a medication time for a pediatric patient. for example my patient will start on "X" medication Q 6hours the timing policy of my institution is 1am 1pm 7am 7pm. the dose was prescribed at 3pm so i started the dose at 3pm how should i adjust the timing of this medication to coincide with my hospital policy?. are there any guidelines related to this issue that can be of further help to me.
Thank you.
Roro.