We only allow early bookings up to three days before the actual event. How to set it?

In the rule settings, select the Shift start from the current moment checkbox. Then, set the period to 3 days.

This will delay the start of the rule by three days from the current time.

If rounding is not enabled, the time will be blocked continuously throughout the day. To block time in 1-hour increments, select Round up to the beginning of the hour. To block the entire day at once, select Round up to the beginning of the day. In this case, you will need to increase the shift by 1 day. For this scenario, set the period to 4 days.

If you want the manager to be able to make reservations without these restrictions, go to Account parameters. Enable the Disable dynamic time boundaries checkbox.

Check the result in the widget: