Welcome back!

Re: minutes/miles per day, I think that's up to you. Maybe start with an out-and-back on one of the trails, so it's easy to turn around and shorten the ride if you feel like you need to. Gradually increase your rides based on how you feel.

What kind of running have you been doing? Maybe that could be your guide to where to re-start with cycling -- e.g., if you can run for 20 minutes, then try cycling for 20 minutes.