DISCUSSIONS on “Rules for online games in HoMM3 and formulas for calculating player rating.”

8+6+1 M
16+8+1 L
30+9+1 XL and Jebus (or 40/45+8+1)

Perhaps 30+9+1 will work for XL if you consider not the fastest players :D, I already wrote my opinion about L, and M, in my opinion, was created for blitz; most people play it with this goal in mind, so the recommended timer should be 8+4+1, and if you want to play macro on M or don't want to strain yourself, you can always agree on any other timer.