Out of paranoia, I wanted to do a test run of an upgrade on my workstation by copying my production install/database locally and giving it a go.
During the process of upgrading the database I kept receiving a message "Fatal error: Maximum execution time of 30 seconds exceeded in ...". The page told me to refresh and it would continue. After numerous refreshes it did not.
So, what I did was edit my php.ini (this is a windows install)
and changed the max_execution_time value from 30 to 120. I issued the iisreset command in a cmd prompt to restart the IIS processes and then returned to the upgrade.
After making these changes the upgrade proceeded and completed. I'm now ready to upgrade the production board to 7.3 as it appeared all of our permissions, etc. carried over ok.
This timeout may not be a problem for others, but we have a very large board with very large amounts of users, forums, and groups. We give customers their own private forums for support purposes so it gets to be pretty busy as each has access granted by groups. Perhaps with all the necessary database work, 30 seconds just didn't cut it for us.
Anyway, I just thought I'd share this here in case anyone else came across this issue.