Can someone please explain what MBT is? Is it measured on a dyno?

It's the minimum ignition timing advance needed to obtain the maximum torque from the engine at a given load, RPM, air/fuel ratio, and temperature.

You aren't always going to be able to dial in this much timing, e.g. because of octane limitation.

So how is this value measured, on a dyno? Can it be done on a road tune??

bump

The best way to do it is on a dyno...a variable load dyno. You can get it in the ballpark on a raod tune, but youre never going to be as accurate.