From my own experience only (after having been learning to play for three years now and still having a long way to go) I don't think this is a great idea.
I have found speed only comes when you no longer have to think at all about what your are playing. If you can read this and play the song at the same time then you should be able to play it pretty fast.
The more you play, the more you become familiar with the licks and phrases that make up most songs. So at first, it is pretty slow going and you need to be patient. For instance, I started trying to learn Ben's Foggy Mountain Breakdown about week 5 or 6 in my banjo journey. I played that song hundreds of times in the weeks after I was finally able to stumble through it. I still play it at least once a day, about 340 days a year. After about TWO YEARS, I started to get it close to speed. It took a long time.
Now, because my hands know more, it is quicker. For instance, I started learning (the tab of) Ben's O Come All Ye Faithfull at the end of November. This is a fast song. Now, four weeks and several hundred repeats of the song later, I can kind of play it at speed (but messy). So it will still take a fairly long time.
Be patient. Really, you have to learn how to walk before you run. Keep on practicing your songs. Practice as much as you can.
Again though, this is only my own experience. You can try to speed practice rolls but I think that would be really boring in the long run. I don't think you could do that two or three hours a day without driving yourself nuts...