Math trick for locking yourself in?

I’m not great with odds and I need a way to pick release dates in a semi-random fashion. This is for self-locking using hypnosis, so there’s room for something more clever than just rolling dice. My idea is to ‘key’ the release date off publicly available numbers. Think Dow Closing figures or the Daily Pick 4 draw. Based on how long you (or your keyholder) want the lockup to last, you can choose a base duration rule. For instance: Want only a 24-hour lock? Choose an odd number. Aim for an average of two or three days? The number must be divisible by three. Looking at one or two weeks? The number should end in seven. Any math enthusiasts with better ideas for a cleaner, more elegant system that offers different ‘tiers’ of duration? Obviously, you risk the lock ending sooner than expected, or lasting longer than planned, but that uncertainty adds to the fun. And if you’re thinking “Chastity Hypnosis? What’s all that about?” it can be quite genuine. There are other threads on the site discussing it if you search around. MP