These rules are evaluated whenever a route is about to be added into a routing table by any dynamic process (dynamic routing protocols or just DHCP). AFAIK, change of state of an already existing route (e.g. when its gateway interface changes state) doesn't trigger evaluation of these rules. I'm not sure whether the rules are evaluated when you add a route manually.
Well if change of state of an already existing route does not trigger the evaluation of these rules, then how do you explain the set-check-gateway=ping property of these rules? They are clearly evaluated AFTER the rule has been added. It would be more probable that these rules are evaluated when routes are determined/selected for packets? Otherwise it would be hard to explain how "set-check-gateway=ping" works. But of course, this is just guesswork.
I have already reported to Mikrotik support about the missing documentation, I think it was at least 6 months ago.