I think it's about 3 weeks, my own is currently having her first season too, and it's driving me mad, i'm forever following her with a scrubbing brush cleaning wherever she's spotted.
Can't wait for hers to be over so I can book her in to the vets to be spayed!
A season can last upto 30 days and sometimes longer. Boo...you should wait at least 3 months after a season to spey to allow for the blood flow etc to return to normal.