In the rule settings, set the Shift end from the current moment checkbox.
Specify a period of 30 days.
This will postpone the end of the rule by 30 days from the current moment.
If rounding is not used, the time will be unlocked smoothly throughout the day.
To open all 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. In our case, you need to set 31 days.
If you need the manager to be able to make reservations without these restrictions, go to Account parameters.
Set the Disable dynamic time boundaries checkbox.
Check the result on the widget: