WWW, you're spot on with limiting your hours - You don't need to be told about the safety considerations or the fact that your students aren'tgettingtheir money's worth.
Here in Oz you're only limited to 6 hrs instruction per day - beyond that, standard flight duty time limitations apply. Lately during an AOC application process CASA Ops Inspectors were telling me that FDT's apply to Prvate Pilots too!
Go Figure...