I would like to model the battery capacity of an energy system such that the battery kicks in when the solar resource is down so that the diesel generator does not go ‘on’ and ‘off’ for short periods of time.   Is there any way to make sure that I don’t have instances of the diesel generator on for less 10 minutes (for example).

Yes.  First of all, if your time step is one hour then HOMER can’t turn the diesel on for less than one hour.  If the time step is ten minutes, it can’t turn the diesel on for less than ten minutes.  Secondly, in a system with a battery, if you are modeling the cycle charging dispatch strategy (look up ‘cycle charging’ in the index of the help system) you can specify a setpoint state of charge.  Then when the diesel comes on and starts charging the battery bank, it will not stop until the battery bank has reached that setpoint state of charge.  That tends to prevent the diesel from turning on for only one or two time steps.