Subtracting two times

I have two times that I am trying subtract and get the difference as just the minutes difference between the two numbers. I have tried to do this several ways but have not found the right result

The first number is in S20, the second number is in R20

at this point:

R=12:39 pm
S=12:59

I don't just want to subtract the times. I am looking to subtract 49-39 and get the result of 20 displayed.

=(S20-R20)*24*60 format as General


Regards, TMS

Thanks for the rep.