I've updated my code, so now I add the GS Reset after the GM ON instead of replacing it, or add both at the very beginning of the first track if neither exists. This only happens if the user chooses to convert to GS.
Per a previous thread ...
https://midi.org/forum/10424-calculating-millisecond-time-from-delta-time
... I am currently not going to worry about the time between the GM ON and GS Reset, as the complexity increases immensely.
For my current project that I am using this for, one of my final steps is running the file through Cakewalk, which ends up spacing out events anyways.
I may also have to figure out a way to add the GM ON in to the soundtrack I've already completed, because Cakewalk did not add those in. I have previously completed all the GS files by replacing the GM ON.