I did mention this:
?(CDate("9:30"

-CDate("9:00"

)*1440
But you need to use Date Variables for the time or use 24 hour format, as 9:00 is strictly 9:00 AM.
Same as doing this:
CDate("3:00"

which is always 3:00 AM.
The same will happen with
lblduration= CDate(CDate(txtTo) - CDate(txtFrom))
You can see this clearly on a machine set in 24 hour time format.
So, everything should work fine if you either use a 24 hour time format when working with strings, or use a date variable.
This is where it is a must to store time in a db field in a date/time field, and not in a text field, unless you have a 24 hour identifier such as 2 digit hours or using the AM/PM identifier.
Same holds true for user input.
Who knows what they mean when they input 3:00, unless they can select AM/PM or know that 3:00 is really 03:00.
jass1220, you need to be a little more observant.
Schweiger did give you a second choice so you only needed to use that, or a variant of that, such as using just "h".
For this, the Hour() or Minute function would be better though.