|Normal calculating time differences is simple a matter of subtracting one from the other, that is providing the fields are defined as Time/Date fields. Time/Date are stored as floating point numbers.|
Providing the clock on time and clock of time are in the same 24 hour period, then there is no problem. Time calculations completely ignore the date.
Problems can arise when the clock-in time and clock-out time span midnight - that is they occur on two different days.
In that is likely to happen you first need to determine if out time is less than in time. If it is, then there is a midnight in the middle.
You will then need to take the difference between in and out and subtract the sum from 24, or 23 hours, 59 minutes and 59 seconds to give you the correct number. 23 hours, 59 minutes and 59 seconds = 0.999988425925926 = the number of ticks since the previous midnight.