I commute 5 days a week and am going to become more dilligent about my weekend saddle time so I would go with the x miles in a month. Weird stuff can happen that can take you off of your commute (wife and daughter going up north for an Ojibwe language bowl so guess who has to skip the commute and car the other kids to school?; you guessed it).
5 (days a week) x 20 (miles roundtrip) = 100 miles in commuting + 50 (estimate could be higher or lower but is the goal) miles on the weekend + 150 miles a week.
Now for May there is 4 weeks so I am going to shoot for the projected 600 mile month. I am actually going to try to eclipse it by adding in some evening miles with the kids.
Time can be such a luxury we don't appreciate. My son races BMX (we just got back from Kearney, NE last evening) and I already lost some commuting miles due to that, we have lots of racing planned blah, blah, blah...
Bottom line I am shooting for 600+ miles in the month of May; am already down a couple of days and will be down a couple more before it's over. We;ll see how it works out and set something a little more impressive for June.
Peace.
Ken