It's similar to the "count to ten" principle, before yelling at someone.
I'd also assume that it may be that having the weekend could put one in the mindset of relaxation and cause procrastination at the start of what could be an intense process that requires drive (depending on individual's circumstances).
Or maybe it's kinda the opposite where if one were to quit on say a Monday instead, there's a good chance that the work week mindset holds, kicks the individual into being productive (maybe more productive than usual out of necessity), and then that weekend would be very much needed to wind down/refresh and reflect on the progress that was made.
Again, just my assumptions, but seem like likely scenarios that could play out
Edit: spelling
If you still want to quit on Monday? Go right ahead...but a lot of times the stuff that seemed insurmountable on Friday, don't look quite so bad with a bit of reflection. Unless they still suck.
What I've encountered: 1. I've never had bigger improvements in my financial outcomes than when I said 'f-it' and pulled the ripcord 2. Doing so dropped my into a stresspit that was grinding me into a red paste, resulting eventually in being Riffed 3. Which let me find a job that, while not great, has good work/life balance and is good for me, at this time, in my walk down my path.
Go into it informed and mindfully and you'll probably be fine, assuming you're in a market that needs you (A french chef in Washington, KS...population 1100, is probably not going to have a sustainable skillset in Washington, KS)
Dad told me 'Never quit on a Friday', but he was also a fan of trusting your skills to support you.