Your PT in rehap will probably put you on the bike right away (although it will be a bent stationary) with virtually no resistance. Good rule of thumb is 6-8mos before cleared for activity. Not to bum you out too much but you will atrophy lots so be ready to work hard at regaining the leg strength (quad in particular). Good news is that you can come back strong from this injury in cycling, just don't give up on the rehab and be sure to state up front to doctor performing surgery (b/c of where he takes the replacement tendon from) and you PT about your goals to return to cycling and at what level of cycling....
good luck