Today Is The First Day Of My Cycle. So After

Today is the first day of my cycle. So after counting I found that my next cycle will be on 9th January. But from10 th Jan we planned some vacation trip. Now I am confused how to delay my next cycle. I am thinking of duoluton l. If I start duolution l from 24th dec then I WL have my nxt cycle on 16/17 th Jan, which is OK,coz I WL be back on 15 Jan. So my doubt is that can I start duoluton l from 12 day of my cycle that is on 24th DEC or is there any day for eating the tablet.