Hi HFTB,
First of all, well done for getting started again. This is actually the hardest part! Make sure that as much running as possible you do now is ENJOYABLE! Don't bust a gut trying to improve your times every run...you'll just end up getting injured again and getting really depressed. Have you got any targets in mind, even if it's just a 5K sometime? I'm surprised you can't find a schedule that suits you as there are loads out there and many on this site...keep looking and you'll find one. In the meantime, yes you could keep doing your 20 minute runs for a while and then step up. Make sure you don't run the same route every time though (or if you're on a treadmill, try and get outside for one session a week), otherwise you'll get bored in a hurry! There's loads of beginners info. on this site which you might find useful.
Have fun and enjoy.
DW