A: Flows are run every hour (approximately). So imagine you have a flow with criteria that triggers an email. Any contact meeting the criteria will receive an email within that time.
Emails in a flow are only sent inside the flow's When to send emails? time window and, if Don't send on weekends is turned on, only on weekdays. A contact who matches outside these times gets the email the next time the flow runs inside them. For example, with Don't send on weekends turned on, a contact who matches on a Saturday gets the email on Monday.