The variable DATE[4] gives the day of the week. 1 for Monday and 7 for Sunday - if this is what you are looking for. You just have to test the variable DATE[4] first, if it matches the day of interest, then further test the time and set the output accordingly.
PIDDEF only needs to be executed once unless you want to change the parameters after sometime. The Integral and derivative historical data will be cleared when PIDDEF is run.