Use Cheat Engine to edit:
01CD8EB4 for the leaderboard playtime (v1.5.387)
01CD8EC0 for the barracks playtime (v1.5.387)
The format is in seconds, so days (86400s) + hours (3600s) + minutes (60s).
I have found that sometimes the barracks retains your REAL playtime (try setting 01CD8EC0 to 0). If this happens you will need to edit 01CD8EC0 to make it up to a whole minute (trial and error, try adding 30 to start with, if it changes try 15 etc...), calculate that playtime in seconds and subtract what you had to add. Then take your target value and subtract your real playtime.
For example: When we set 01CD8EC0 our real playtime shows 00d 11h 54m... we need a value of 11h 55m for it to be accurate... so we add until it turns to 00d 11h 55m...
if it changes at, say, 34, then we now know the real playtime is 11h 54m 26s...
So, if we want the playtime to be 7 days 2 hours and 12 minutes:
7 x 24 x 60 x 60 = 604800
+ 2 x 60 x 60 = 7200
+ 12 x 60 = 720
TOTAL TARGET = 612720
Enter this straight into the leaderboard... then, if required, subtract the real playtime to get the value for the barracks...
11 x 60 x 60 = 39600
+ 55 x 60 = 3300
TOTAL REAL = 42874
TARGET (612720) - REAL (42874) = 569846, what we enter into CE...
Play a few rounds once done and check that both times have changed and are in sync...
Hope this helps abit...
---------- Post added at 04:30 PM ---------- Previous post was at 03:20 PM ----------
Oh, you can also clear your real playtime in the barracks by...
1. Going to prestige 15 (01CD8E64)
2. Adding 1+ tokens (01CDACC3)
3. Going to the 'Prestige Shop'
4 . Selecting 'Reset All Stats'.
Then you can just stick the same playtime value into both. You will lose all your setups/other stats though...