Haven't seen this mentioned elsewhere here.
Doing some Audax related searches and ended up on Randonneurs USA (RUSA) site and saw a post regarding changes to ACP BRM rules and subsequent change to RUSA rules. Bottom line is that for them all Intermediate Checkpoint opening & closing times are now only advisory with only the final checkpoint actually counting. Can't find anything related on ACP site but their "news" items are years old.
https://rusa.org/node/1667
I guess it is up to each region to decide to follow ACP lead or not
PS - Also "ACP Super Randonneur Award - now calendar year" https://rusa.org/node/1677
I don't have the rules memorised or a rule book open in front of me but my approach as an org or rider is
1/ if you get to a control and it is closed, get proof of passage anyway. You might make up the time later
2/ consider however that if you are so slow that you can't make the time for an intermediate then probably you are doomed
3/ orgs are fine to close, lock up and drive away from controls if they are ended even if there are riders out there. As a rider you are just going to have to fend for yourself (including proof of passage)
There are some routes with a slow / hilly / difficult bit near the start where finishing might be possible even if you miss the intermediate time
OTOH if a rider gets to an intermediate
too soon and ahead of time then they absolutely must wait until the control opens before controlling
Not sure what I would do as an org if someone broke this rule and turned up at the end with a otherwise valid card
Only remember it happening once on my events, I was at the intermediate control in question and they were about 1 minute early