Well it depends on which of the following categories you fall under:
1) International student in the US on an H1B
2) International student in the US on a visitor visa
If you're (1), then there's a thread on this forum discussing exactly that. I'm not quite sure what the exact process is so I'd recommend that you check there.
If you're (2), then the whole process shouldn't take longer than 3 weeks. Basically the stems are as follows: getting your finances in order, sending those through to Cornell (delivery delay), waiting for them to issue an I-20, Cornell sending I-20 to you (delivery delay), you paying the SEVIS fee online and booking an appointment with the consulate in your area (I'm not sure how you'll handle this since you're already in the US), giving an interview and getting stamped. All done.
A lot of the other schools are hoping to wrap-up their watlists by the end of the month and I'm guessing that Cornell will do something similar too. Not sure but either way, nothing to worry about... you have plenty of time in terms of processing your F1.
Thanks for the info redjam. I was thinking around 4-5 weeks but no surprises in the process.