Gotta be careful with stress fractures, as they often can be trickier to recover from than a completed fracture. Most important is to bear as little weight as possible on the fracture at first [3 weeks] and then over the next several weeks very gradually increase weight-bearing [first in duration, then in intensity] to encourage proper bone recovery. Light cycling at 4 weeks will probably be alright, depending on severity. Definitely don't rush back into running.