I am an experienced female chastity belt wearer. I have worn a belt 23/7 for over 6 weeks at a time. I say 23/7 bc I would be unlocked for an hour to take my enemas, a shower, clean my belt and do my fore and aft exercises. I was usually double plugged. Also of course, I was not 23/7 when my Sir wanted me unlocked and available. Practice beforehand what regular voiding is like and how you are going to handle the usual 'wiping moisture' (Also many women are allowed to be unchaste for the week of their period, some can use a super tampon for the day and some use a cup.)
I would not suggest trying to wear a chastity belt for such a long time til you work your way up to it. Some can not handle them for even 12 hrs. Fit is important and it takes a while to get a comfortable fit. As well there are many brands on the marker with so many options.
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When it comes to KH, many couples are each others KH. There are many methods of keyholding. Some involve mutual keyholding and others are for singular or emergency access...........
1.Mutual KH is obvious
2.Insert key in a small brick of plaster when wet. Put it on a rarely used shelf or in a drawer etc. If the key is needed, the plaster will break with a smash to a hard surface. A sealed piggy bank is another option.
3.Place the key in a "letter wax sealed" (like in the old days) thick piece of card stock. He or she can carry it to work and show the untampered casing when arriving home.
These are just a couple of options. There are -so- many more listed on the net.
In an medical emergency needing a trip to the ER they will just use their (always handy) tools to remove it be it a $70 leather one or a $5000 Carrera. (They've seen it all.) It would make me cry to see a Carrara damaged though.
In summary and my opinion only: Work up to 4 days. Know that 4 days with out bowel movements might be hard even with a high colonic before the fun starts. Be each others' KH and if separated carry your own in a tamper proof container (until you are experienced).
Enjoy. Have fun. Be safe.