午夜到达时，List 列表项中的AddDays（1）

I have a problem, have a list of datetime collection, combined with date selected from drop down but time slot is added from 7am to 4am (21 hours). I want to fix the date in this collection in a way that if reach to hour 00 or 24 (12AM midnight), the the date should change. I have a problem, have a list of datetime colle