Appointment lower limit setting specific for each Service Provider

Hello,
I'm asking your help in understanding how I could achieve the result described in the title.
I know A+ let me define a single lower limit setting, valid for all service providers.
But I urgently need to set a lower limit for a single service provider, and actually I cannot figure how to do it.
Can you help me show ? Have you got any code snippet I could use ?
Thanks as usual for your valuable help
Kind regards
Antonio