These are great sections to start with.  Maryland does have some sections with a lot of rocks, but the up and down is a bit more gentle.  Mileage estimates depend on how comfortable you are with what you are carrying, how well your shoes work for you, and what have built up to.  If you know how many miles you typically would hike in an hour and how many hours you would reasonably hike, you could start there.  I then consider terrain and elevation which you can get from a map.  Maybe add 45 minutes/ 1000 ft?  And don't forget to take breaks even if you don't feel like you need them.  Just sitting for 15 minutes and loosening your shoes can make it feel like your starting fresh again.