Thank you both for your assistance, but my question is still left un-answered. And I have no idea how to better explain or get to the answer I need. From what I've seen, most are under the impression that a military date time group (DTG) is represented by DDMMMYY HH:MM. However, this is very much incorrect.

With the US Military DTG, the following is represented:

DDHHMMMMMYY
DD = Date
HHMM = Time (in 24 hours format)
MMM = Month
YY = Year

FD, your formula changed all dates to the first day of the month. The rest of the formula converted someone correctly.

Shg, what you suggest only shows a 1 hour, 15 minute difference. In reality, by looking at the day(s) in the example, it should be a total difference of 39 hours. Your formula does not allow for the advancement of time into the following day. 8:10 AM on Dec 6, to 11:10 PM on Dec 7 is a total of 39 hours.

Again, thank you both for your assistance, but it looks like I have a lot more research to do.