Yes, it does make a difference. My commute is about 22 miles (35 km) roundtrip, 3-5 days/week depending on weather and my work schedule. On the weekends, I usually ride 50-60 miles (80-100 km) with my friends. I used to ride just as often on Saturdays, but generally shoot for Sundays since I started bike commuting. I need Saturdays off so my legs can recover from commuting. Occasionally I do my long ride on Saturday if the weather forecast is bad for Sunday, and I suffer on those days. Another trick I've learned is to ride at a really easy, recovery pace on Friday.