I should've posted this here earlier, skFreeze is allowed, and it fixes the issue: https://github.com/Halamix2/StuntKit_modules

Yeah, after testing I couldn't get this freeze on Windows 7 (even with StuntKit skScreen)
On WIn10 I get freezes on D3D and Glide versions (through nGlide)
It is synchronised with Windows uptime (freeze at 07:09, 14:18 and 21:28) (give or take few seconds)

Didn't help:
• Disabling Windows Defender
• Windows 98 compatibility mode

It's not v-sync related, always 7m 9s independent from the frame rate, it seems the freeze happens everywhere, in game and in the menu, so something global is causing it.

Freeze lasts for 0.500ms, +-40ms (I know, I should've enabled 3 decimal places, not two)
I have counted 7m 9s 500ms +-40ms, still correct with your measurements in the margin of error

And it seems it's 7m9s between freezes even if you turn off the game completely and turn it on later, might be some Windows stuff

Great finding!
As to why does it happen - I don't know, for now it's certainly not frame counter overflow, physics always run at 60Hz.
7m 9.7s would be about 25782 +- 6 frames, nowhere around int16 limit

I'll try to measure that on my PC, as I have 100Hz monitor, if that was related to v-sync then I should get freeze earlier.

I personally I'm against it, IMO we have clean and any savestate subcategories mainly to allow all or only "stock" cars, but it's just my opinion

I have added IL with "Exhibition single lap" category:

Exhibition mode

No CPU players

any number of laps

Record whole race, the time of best lap will be used

If we were to add IL I think Exhibition mode would be better than Time Trial, as all tracks are available. Option B sounds good, just selecting one best lap out of 9

Championship was split into clean and any savestate subcategories, we don't know yet what to do with Arcade

The existing autosplitter for Livesplit was only tested in Arcade mode, but it works there good enough (from name to last finish line)

Emails have broken banner image and copyright date of 2017:

There is a timer that counts time of the whole race, it starts after countdown and stops at the finish line

It seems that the game logic always runs at 60hz and that timer also beats 60 times per second.

I've made proof-of-concept IGT autosplitter and tested it on Arcade (clean save).
During test, the time measured by autosplitter was 0.08s (80ms) longer than times stored in save file, so while it's close to the gametime it's not ideal (yet?)

Edit: Now autosplitter should have the same time as save files, I'll update it in resources in few days after some testing

Arcade mode - current rules just say "Complete any path of Arcade mode. Clean savestate is required, backup your progress and reset the game beforehand."
But the game expects player to finish 1st to complete arcade mode with "success" screen, so I'd say we could change that rule to
"Complete any path of Arcade mode. Last race have to be finished on 1st place. Clean savestate is required, backup your progress and reset the game beforehand."

Game save is stored in Game location, usually C:\Team17\SGP\save\card00\setup.bin
"Clean savestate" means removing that file, so that no cars or tracks are unlocked, because current "any savestate" record uses car (Team machine) that needs to be unlocked in Time trial mode.
You can copy that file to safe location and remove it from the game directory, and restore it from copy after speedrun.

OBS can record videos and you can add many windows that will appear on the video. OBS usually makes way smaller videos than Fraps but requires some setup. For instance, OBS recording at 720p 30fps and 2500kbps bitrate, it takes around 200MB for 10 minutes, so full Championship run (~2hours) would take around 2,5GB. I use OBS for recording, DxWnd for running Stunt GP in window and Livesplit for timer.

Arcade: "Track unlocked" adds about 1-2 seconds of delay, I haven't timed it precisely, but given that some records are just 2 seconds apart (taking obsoleted runs into consideration), I'd say it would be good idea to require clean save, as in player can set audio volumes and camera settings beforehand but cannot have any progress in Arcade mode.

Championship: I think it's unfair advantage to use team machine, but maybe splitting championship into two categories would be a good idea? Clean save and unlocked.

100%: I also don't know what that means, however there is a car (Team Machine IIRC) that can be unlocked in Time Trial under some specific conditions (I forgot them :/). So maybe 100% mode could be referring to finishing all connections in Arcade mode, Championships and unlocking all cars and tracks? Proof in form of opened Catalogue with everything unlocked after the timer was stopped would be nice, but it might not be necessary.

I've made a push request to Hoxi's autosplitter, so it starts counting after exiting "single player" menu, splits at the finish line and resets after coming back to single player menu

So for Arcade I'd suggest starting counting after selecting option in single player menu and finish counting after crossing finish line of the 4th race.