Your best way to get fit for general cycling is to do it every day! This takes no time at all if it is your daily commute. Then, after some weeks or months your daily run will take half as long, and occasional long distances will be easily within reach. When I returned to cycling with a six mile commute, my 45 minute run became 25 minutes regularly, without need for a shower on arrival! and after a few months, a sixty mile Sunday ride was achievable.