- You can get padlocks & even handcuffs with timers on them, some of them are pretty heavy duty, if you don't want to make a trip to the hardware store you can order delivery online.
Combined with a strong cellar door (or a heavy duty steel security door if you must) & there really shouldn't be a problem. Just be sure you put all the tools out of the room before locking yourself in.
None of that stuff is particularly expensive & is all pretty easy to get hold of.
- The other really obvious precaution is to have really big pig-out the day before the night of the full moon, when I say 'big' I mean unreasonably humongous, that's stomach stretching "I'm in no condition to do anything but lie here & be very still in case I hurt myself" huge.
You've said they're psychologically like ordinary wolves during this time & wolves don't hunt when they're stuffed.
- Drugs, off the shelf sleeping pills & whatever else they can get hold of so they sleep through the full moon, a helpful doctor friend (or relative) might be good but so much of this can just be bought online & delivered by post that it really isn't isn't necessary.
A practical knowledge of wild herbs can also stand in for this.
- And finally something topical, "social distancing", go camping.
Make sure you're over a day's journey on foot from the nearest people before the full moon & that you've no other means of transport to hand.
Of course you can combine all four of these with a good solid concrete bunker somewhere in the wilderness miles from anywhere.
Edit : A timed lock for the medieval era.
You might not think timed locks are very likely or easy to come by in a medieval setting.
But, then again, perhaps not.
First find yourself a cave.
Then you need a big rock (too heavy to move unaided & big enough to block the cave).
Now you'll need some rope some wooden pit props a source of water & something to sling your rope over, this all needs to be outside the cave.
Sling the rope over your 'something to sling a rope over' & tie the rock to one end & the bucket to the other such that your bucket is hanging in the air over your head, fill the bucket with water so that you can now lift & move the rock, place it over the cave entrance & wedge the pit props under it to keep it there when you empty the bucket, you know have to arrange for water from a nearby water source to drip into the bucket (you're going to need some piping).
Enter the cave kick out the props (or tie ropes to them & pull them away) & the rock slams down locking you in until the bucket has filled enough to let you move the rock.
Some experimentation with bucket size, drip speed & what have you may be required to get the desired timing.
Voila! & there you have it, one crude water clock locking mechanism.