In general I like this concept. However, one can discuss if 6 months is always the right amount of waiting time.
I think there are 4 ways you can see it:
1) There should be a fixed amount of time
2) In the beginning the waiting time should be longer to ensure the wearer gets a proper feeling of what it is like to be chaste but it can be shorter the longer he/she has been chaste because then asking for getting the belt off is unlikely due to horniness and more likely for a serious reason.
3) You take it the other way around by saying that the longer someone has already been chaste the longer he/she can endure a longer waiting time period.
4) There is no exact plan on when this waiting time should be how long. Instead you trust your keyholder to chose an appropiate length of time for it.
No matter what you mutually agree on I agree on the fact that proper wearing has to be trained beforehand.
Then there should be enough trust between the wearer and the keyholder and therefore I would prefer option 4.