12 hours seems reasonable but technically if he was really determined to drink he could have a glass or two and maybe pass after 3 to 5 hours. It all depends on the person . Look up bac levels and time. I think the rule of thumb is for every glass it takes an hour to sober up but it really comes down to bac timeframe.
Also I want to add that if he uses mouthwash without waiting awhile itll read fail and ive heard a few other things can do it too.
The camera one is a good idea though I think I would do maybe every 6 hours give or take instead of 12.
Having been familiar with breathalyzers. Having young children and an alcoholic co parent 6 sits better with me than 12. Imo
Maybe start with every 6 hours and after a few visits or so work way up to 12 .....