Let's say you have a 24-hour hourly rental.
Create a new tip.
1. Enter a name.
2. Enter the message for the minimum duration warning.
3. Select the type - Error.
4. Click the Constraints tab.
Set the total number of rental periods to be less or equal to 1.
This will show this tip only when customer has booked less than 2 periods.
And this is what we actually want.
This is the configuration you will get:
Check the result on the widget. Try to book only 1 hour: