I've been doing a bit of reading about this myself. I've read that ketosis kicks in when all your glycogen stores have been used up so it depends on how you were eating before you started. I imagine it wouldn't take more than 4-5 days.
Some signs are different smelling breath (some say sweet, some say bad), increased energy, different smelling urine/BO, thirst and an odd taste in your mouth. I'm experiencing the taste in the mouth, its been around since this afternoon and didn't go after cleaning my teeth and mouthwash and a mint later on. Feels a bit like i have metal in my mouth or something a bit tart.
FF :]