For both Free and Premium, invitation emails/text messages are sent out immediately. If there is any delay with our systems, such as with a high influx of invitation events going out at the same time, we will put a note on our Support Site stating the delay. Invitations and notifications are most likely to have a delay on Thursday mornings, because of the high volume of events on Saturdays, and that is when our automatic reminders go out for thousands of events, which can delay the system for a few hours.