The date and time you select will also serve as the cut off point for any additional contacts who meet the starting criteria. For example, if a contact meets the starting criteria or is added to an "Active" list at 12:01am on the date selected, they will not be enrolled or sent an email. The easiest way to think about this is when you send a one-off / scheduled email in HubSpot, you have to select a time that you want your email to be sent and after that point, anyone who becomes part of the list(s) you selected will not be sent the email.