I started riding on a 10 mile loop in George Bush Park next to my neighborhood. 4 miles gravel road, 3 miles trail, 3 miles paved. When I first started I could barely finish. I started going regularly a couple weeks ago and was able to do it in about 60 minutes. 2 days later I surprised myself by pushing hard and making it in 45 minutes. I assume that isn't to shabby on a mtb, especially since I pass road bike guys on the paved part already.

What time should I get to before increasing my distance? I was thinking I would work at getting down to 30 minutes, averaging 20mph, then increasing my distance to 20 miles and work hard to get down to 20mph average again with twice the distance, then repeat with a longer distance.

Is this a good plan? Anything I should do different?