Time formula help

[Kiwi den]

I would like help with a formula to solve the following
Cell A:1 = 7:30am Cell A:2 = 14:00

I want Cell A:3 to equal cell A:2 - A:1 but if the time spans 12:00 to 12:30 then to deduct the 30 minutes from the total time in cell A:3

Your help appreciated

 

[Yongle]

Is the underlying cell value (regardless of display format) date and time ? OR time only ?
- test by putting this formula in a different cell =A1-1
- if the formula returns a cell full of hashtags (even if you widen the column), then A1 contains time only

This formula works for both
=IF(AND((A1-INT(A1))<=12/24,(A2-INT(A2))>=12.5/24),A2-A1-1/48,A2-A1)

This formula works where A1 & A2 contain time only
=IF(AND(A1<=12/24,A2>=12.5/24),A2-A1-1/48,A2-A1)

NOTE
The values in A1 & A2 are both assumed to belong to the same calendar day

There are other ways to to this- here is a link illustrating calculation of time differences