To calculate the appropriate IEEE 802.1D STP timer settings for Max Age (MA) and Forward Delay (FD), you only need to know the Network Diameter (ND) and Hello Time (HT). Plug the values into these two formulas:
MA = 4*HT + 2*ND - 2
FD = 0.5*(4*HT + 3*ND -0.5), and round UP to next whole number or integer
For STP defaults, HT=2 and ND=7, so MA=20 and FD=15 (14.25 rounded up to next second is 15). STP reconvergence will take from 2*FD=30 to 2*FD+MA=30+20=50 seconds.
In your case, HT=2 and ND=10 results in MA=26 and FD=19, and reconvergence in 38 to 64 seconds.
To speed up reconvergence, you could lower the HT to 1 second. That would lead to HT=1 and ND=10, MA=22 and FD=17, with reconvergence in 34 to 56 seconds. It's not really much of an improvement, though. You would be better off minimizing the size of ND.
What switches is your customer using? Maybe IEEE 802.1w Rapid STP would be an option.