The key is understanding how Excel stores dates and times. They are really stored as large numbers.

To see this, go to any valid date/time entry in Excel, and temporarily change the cell format to "General". This is how Excel actually stores and sees the dates/times.

Making it a date is just applying a special format to the cell (and formatting does not change the value, just the visual representation).

The integer portion of the number is the number of days since 1/0/1900.

And time is just the fractional component of one day.

So 3:00 AM would just be 3/24 (as there are 24 hours in one day), which simplifies to 1/8.

In Excel, the INT function takes the integer value of a number (meaning it drops the decimals). So if we want to get just the time piece by itself, we can take our original number, and then subtract the integer portion of that number, leaving just the decimal piece (which is the time piece).

I hope that clarifies things. Let me know if you have any other questions.