Excel Macro - Date/Time functions - Overtime Calculator

What I'm trying to do is calculate for overtime.

Cells D12 and c12 contain times.

C12 = 8:00 AM
D12 = 5:45 PM

=(MINUTE(D12-C12) / 60)

Works as expected. Returns 0.75

=IF(NOT(D12 = ""),IF(D12-C12=0,"",(HOUR(D12-C12) & "." & MINUTE(D12 - C12) )- 1),"")

Works almost as expected. Returns 8.45

=IF(NOT(D12 = ""),IF(D12-C12=0,"",(HOUR(D12-C12) & "." & (MINUTE(D12 - C12)/60) )- 1),"")

Fails with #VALUE

What am I doing wrong?