I'd have to go back and read my posts in other forums to tell exactly how long it took to get back on a real bike but I believe it was a few months. The biggest fear (that my PT and doctor had) in my case was that trail riding I would put down that leg for recovery/turn situations, not a good thing to do early in the game.
I was also allowed on a road bike (or in my case riding mtn. bike on road) before trails. I did ride some gravel roads which are in my area, but all the biking was done wearing the brace, in fact I went out last weekend for the first time without wearing brace for bike riding since surgery. I bought one of those "bike in your living room" gadgets from REI and as soon as it was O.K. with PT I would pedal the bike everyday and make it a good hard ride. I think this really helped recovery quality and time.
The most difficult thing for me in the whole process was not doing the usual push the limits, the repair was worth giving it all it needs. Short time frame in the overall scheme of things.