Listen to the body and go as often as you want; want being the operative word. Subscribing to "should dos" is a sure fire way to turn cycling into a chore.
Plus, dont be afraid to adapt your ride on the hoof. I've lost count of the number of times I've been "up" for a ride, set out for a decent stint, but after a few miles realised that I probably wasn't as up for it as I thought and a planned 50 turned into a leisurely 5. Equally theres been times when I've thought I cant be bothered to put in much of a shift, I'll just spin the legs for a few miles to get some fresh air, but once in the saddle felt so comfortable that the opposite happens.