Matt gives up sexual contact etc. for Lent hence 40 days and forty nights, but the season of lent (Ash Wednesday to Easter Sunday) is 46 days and 46 nights because Sundays are not counted. If Matt gave sex up for Lent, he would go 46 days and nights in a row without sex. If (as is listed at the bottom of the screen as "day # blank") he only went 40 days and 40 nights, he would be cutting out the Sundays and could do what he so desired with those days.
After Matt goes into his meeting with an erection he is shown in tan khakis, when Ryan gets up and tells him his "little friend" is showing, they zoom in on Matt's erection and he has on dark blue/black pants.