We no longer "make up" any missed access, and as our rota is now Thurs pm til Sat lunch each week, we simply wait for Thurs to come round and then start again.
I still don't get the " keys" suggestion though. There really is no point in DSS coming to stay at our house, as per the rota, when we're away, simply to be rota-compliant. Firstly, it would mean his mother having to drive him over to our empty house, secondly access surely means the parent/child spending time together, not sitting in Dad's empty house, and thirdly - we wouldn't be happy with DSS being in our house in our absence. Because he doesn't live at our house he's not very familiar with our electrical appliances (ie the grill) and we wouldn't consider him safe (and I could imagine him running a bath, and then forgetting about it, causing a flood). He's not good with keys either, and we couldn't rely on him to lock up in his way out.
We're going on holiday soon, for 7 nights from Saturday-Saturday; DH has already made DSS aware if this. On the week of our departure, we'll have DSS to stay on the Thurs night, and that will be it. The ex enquired why we aren't having him on the Friday night, as we don't fly til Saturday. But we have a 7am Saturday flight from Birmingham, we're leaving the house at 2am on Saturday, and it would seem insane to drop DSS back home in the small hours, just to ensure the right quota of nights is achieved that week. Thankfully DH agrees, but this is how silly "extreme rota" can get. And don't forget DSS is 18 ......