Haven't tested this, but looking at the snapshot above, you can try something like this:
IF [TimeSlot (group)] = 'PT' THEN [Show PT]
ELSEIF [TimeSlot (group)] = 'LN' THEN [Show LN]
ELSEIF [TimeSlot (group)] = 'APT' THEN [Show APT]
EDIT: If they are calculated fields then you might run into 'aggregate' 'non aggregate' issues, in that case you will need to make sure both the fields you use in the calculation are aggregates.