Use five checkboxes instead.
Create an expression binding somewhere.
if({../chkMon.props.selected}, "1", "0")
+ if({../chkTue.props.selected}, "1", "0")
+ if({../chkWed.props.selected}, "1", "0")
+ if({../chkThu.props.selected}, "1", "0")
+ if({../chkFri.props.selected}, "1", "0")