Validate a Date/time field to be within certain hours (i.e. 9am - 5pm)

If you have a New Responsive form and you use 24 hours format. You could do something like:

Create a variable: StartTime - Type String: 
formatDate([Form].[dtStart],"HH")

Create a form rule: Business hours:

if convertToNumber([Form].[StartTime]) >= 9 and

   convertToNumber([Form].[StartTime]) <= 17

Then do something like:

Label1 value is:  Business hours

Else
Label1 value is: Outside business hours