He proposed 90 days, and I agreed. I should have pressed him for longer. I'm thinking a year would have been better.
I made him determine the length of time. I played hard to get and told him if he really want my to be his Keyholder he needs to prove it and show me he's serious. I was expecting a month. When he said 90 days I was shocked and I immediately said yes. Knowing now what I didn't know then.... He's in the dog house now so I'm going to leave it be for a little while.
You can always negotiate an extension. Or alternatively, agree it carries on indefinitely unless and until he gives 90 days notice instead if he wants out.
For some reason, even thinking about a year makes me shake with fear...and I wasn't even the one threatening with it!