stop a new record creation based on a field value

Do you have a dropdown or anything to select a different type of request? Like one that had PTO/Vacation and another entry for Unpaid?

If you had that then you could use a form rule or table custom data validation to prevent the user from saving the record. For the form rule you would want to do 'when the record is saved, and if the Request Type(or whatever you have) is for PTO/Vacation and they have less than 1 hour available, or less than half an hour, whatever your limit is, abort the save. Then give a reason for the abort.

Here is something about custom data validation. https://help.quickbase.com/user-assistance/custom_data_rules.html

The custom data rules give you a lot more flexibility than the form rule does. These should also work if the user is adding things that are not from a form as well, whereas form rules only work on the form itself.

If(

[Request Type] = "PTO/Vacation" and [Vacation Time remaining] < 1,

"You do not have enough PTO available to make this request, please submit this as Unpaid time off."

)

Something like that should work but you may need to jiggle it around a bit to get where you want.