Not Passing motion

Dear mummies My newborn is 1mth4days old.. I mix feed him. Recently changed his FM to Nan optipro. He was previously on Similac.. It has been a little over 24hrs since he passed motion.. Is he constipated? Is it the milk? How long can newborns go without passing motion?I do massage his tummy after each diaper change but still no result. First time mom, so worried here.