You can block the time selected on the calendar in two clicks.
To do this, you need to make a small pre-configuration.
Let's say we have such a resource:
Create a new Not available rule with an empty schedule.
Move this rule to the right as it should have the highest priority to overlap the rest of the rules.
You will get the configuration like this:
Now go to the order cart.
Click Block time.
Select the resource and time you want to block.
After that, you will see a drop-down list of unavailable rules.
Select the rule you created and click Add period.
This time will be immediately unavailable.
If you want to unlock this time slot, simply delete the created period from the rule.