I've made an autosplitter and load remover for the PS1 version of the game. This does not start the timer at steamboat or stop the timer when Pete is defeated, but it splits after every mission (or it has an option to split after every screen), and it removes load times from game time (this can be turned off).

The autosplitter is found at https://pastebin.com/FmEYGjHm Copy everything in the pastebin, and paste it into a new file called LiveSplit.MickeyMania.asl. In Livesplit, edit layout, add Scriptable auto splitter, and browse to the file. If you did it correctly, options will pop up.

This is for emulator only, so we are not gonna change timing method to loadless. The memory addresses that I'm using are from ePSXe 2.0.5, BizHawk 2.4.2, and Retroarch 1.7.3 (Beetle PSX and Beetle PSX HW cores only, requires uncommenting). If you're using a different version or a different emulator you might have different addresses, and there are instructions in the file to find the addresses you need. It's not hard to simply change the addresses, but contact me on discord if you need help.

I'm not gonna make one for SNES or Genesis, but if you want one, you can find some relevant addresses and contact me, and I'll adapt this. Not sure how it works on those platforms, but for PS1 there is a variable that starts at 0 (for steamboat) and increments on every screen (1 for wharf, 2 for outside lab, and so on). Another variable is 1 when there is a loading screen, and 0 when there is a menu, cutscene or gameplay. If you want an autosplitter on your platform, try to find some variable that behaves similarly.