HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

Please help with the timer during the game; I can't figure out which keys to use to change the time value...

Thank you in advance!

The numbers on the top row of the keyboard should work. Num-pad support will be included in the next version of the HD mod; I've already given Baratorch the fix.
If the numbers on the top row don't work, it might be necessary to change the keyboard layout (although it shouldn't affect anything), and check for any programs that might potentially change the layout.