What I like to do is create symbolic constants for the days of the week.
On the Doc Editor, click Symb button to create a Symbolic Constant (one for each day of the week)
So,
Sun equals the decimal constant 0
Mon equals the decimal constant 1
Tue equals the decimal constant 2
?
Sat equals the decimal constant 6
THEN I your Ladder Logic, replace the .DayOfWeek comparison (right side) from the decimal constants to these symbolic constants (Mon and Thu):
]SDT0..DayOfWeek >= Mon[----]SDT0.DayOfWeek <= Thu[
and the code reads much better. Attached is a screen shot. Note how the "Extra Info" field reveals the constant value above the symbolic name (nickname), so you get both the symbolic name AND its value!