How Can Periods Be Postponed?

I want to delay my periods for a month, my doc suggested me to take DUPHASTON 10 mg 12 hourly fr 21 days right after periods n then stop n let periods come. Can DUPHASTON taken fr more than 21 days ??? What if after 21 days I get delayed periods ? Right now my cycle is regular ... I need to delay periods (skip 1 cycle ) fr pilgrimage , plz suggest ...