It is not possible to answer this question with guaranteed values. However, if you have a single MSTP region, then the MSTP convergence time is quite the same as with RSTP, and you can expect the convergence to be very quick, depending on the nature of the topology change:
In a well-designed network, RSTP/MSTP convergence should occur well under 1 second, but the actual mileage may vary depending on the actual design of the network, the extent of the topology change and the intensity of its reoccurrence, and the CPU load on the switches.
My two cents. Please feel welcome to ask further!