i'm assuming you haven't been riding or doing cardio of any kind, for very long?

if so, the weekend ride will do just fine. and what the folks say about increments threaded onto your regular distance will be no problem.

for most people that are even able to actually ride a bike, anything that doesn't involve drastic intensities or distances will be no problem. what is "drastic" varies, but if you can ride your route at minimum distance, adding a mile or 3 won't hairlip you at all.