The highlight thing is real but it's not the stand part doing it, it's the 1:100 dilution. Rodinal is a compensating developer at high dilution no matter how you agitate it, so you'd get that softer highlight rolloff even with normal agitation. The shadows opening up is the stand part though, since the developer exhausts in the highlights and keeps working down in the shadows while it sits there. As for timing, most folks just pick a time and stay with it, like 60 minutes at 1:100 is kind of the standard starting point. You can push it to 90 if you want more punch but you're not really guessing so much as tweaking one variable at a time.

My sister had something like that happen with a horse trailer hitch, not a leash, but the same kind of wake up call. She pulled out of the drive with the trailer hitched but not locked down all the way, and it popped loose at the first stop sign. Nobody got hurt, but she drove straight to the shop and had them weld on a backup chain setup that same afternoon. It is funny how one close call changes what you trust. Four years of good luck can make you forget that gear wears out.