6 years too late with this but here we go...

During my most recent runs with the double-strafe speed glitch, I've noticed that the start time probably isn't the first non-black frame. I edited a quick comparison that shows the player gets control around 0.67 seconds before the first non-black frame. You can use , and . to scroll frame by frame in youtube. The timer on the left starts on the same frame that w is held. Ensuring that it exactly counts the amount of time that the player has moved. The video on the right starts the timer on F12 press. I synchronized the video to where both left and right video reach exactly 4 ceiling tiles visible on the same frame. It is worth noting that they de-sync by a frame soon after for seemingly no reason.

While not exactly "easy," the easiest solution would be to add 0.67 seconds to every run. This is a problem for any runner that has submitted a time that beats their old time by less than 0.67 seconds, the leaderboard will then make the older run their new PB. We'll have to update their older runs too. Well actually the easiest thing is to do nothing, just make sure you're moving before the timer starts for WR attempts. The end time is arbitrary as it is, why not the start as well. shrug Side note: If you hold keys too early during a reset, they wont register, but I was clearly able to hold w before the real start time on the video on the right. I'm not sure when is the earliest you can hold it, but I'm glad we don't have to make frame perfect w presses at the start.

Okay, you got WR and can do frame timing so you can be a super mod and figure this out. I'm not active anymore as you can tell by the fact that it took me a year to reply.

I suggest you do absolutely nothing. This game gets scrub runners submitting to it and adding esoteric timing rules would be confusing for them. It's simpler to say that you can start moving before timing begins. If you do end up changing anything make sure to be very clear about the new timing method and get confirmation from all active mods.

Also it would be helpful for noobs to put that video in the guides page to clearly document being able to move during the black screen.