When should my period start??

I just started taking TriNessa Lo this month and I am on day 3 of the green (placebo) pills and still no period. I have always had irregular periods (one of many reasons to start taking the pill) so I'm used to my period being late and I'm not too concerned about pregnancy because we've been using condoms. However I would really like to know when I should expect my period. Does it usually start on day 1 of placebo pills or later in that week? Should I be concerned if I skip a period altogether while on the pill?