Using your example where a client is on retainer for two floating days per month, how do you avoid clients making urgent demands for that time? I fear having a number of clients pre-paying for time each month and then the last week of the month those that, for whatever reason, didn't use their time, staking claims.
1) In my experience - it doesn't happen.
2) The way I set it up to alleviate that fear, before I saw that it didn't happen, was to separate the booking time from the delivery time. So $client gets N days each month when they can ask for a booking, which will then get scheduled in over the next 30 days from the point they book it (so if the client requests N days on April 15th, they get booked in any time from Apr 15-Jun 14.)
1) In my experience - it doesn't happen.
2) The way I set it up to alleviate that fear, before I saw that it didn't happen, was to separate the booking time from the delivery time. So $client gets N days each month when they can ask for a booking, which will then get scheduled in over the next 30 days from the point they book it (so if the client requests N days on April 15th, they get booked in any time from Apr 15-Jun 14.)