How To Switch The Time Of Intaking Tegratol Retard While In Different Time Zone?

Hi, I hope you can help me. I am on Tegratol Retard 500mg for epilepsy. It is taken 500mg at 8am & 8pm. I am going to the states for a holiday in April. What times should I take it at? Should I switch to American time straight away or do I have to work backwards to keep a 12hr gap between doeses? Thanks Mary