Hi ,
Assuming that you have 3 named ranges :
Check_In , which has the time value 6:00 AM
Check_Out , which has the text value 18:75 PM
Working_Hours , which has the text value 08:00
the following formula will give the result 4:45
=TIME(LEFT(Check_Out,2),(RIGHT(SUBSTITUTE(Check_Out," PM",""),2))*0.6,0)-Check_In-Working_Hours
Narayan