It definitely takes longer than 3 days to become physically dependent. You might feel a bit shitty after 3 days of use, but it's not withdrawal symptoms. Withdrawal is similar to benzo withdrawal as Ambien has a similar mechanism of action (binds to some benzo receptors) but it seems to cause dependence more slowly than benzos do and the withdrawals seem generally to be less severe. Of course it would depend on how much you take, how frequently and for how long though.
If you have been dependent on benzos or similar drugs in the past you may get withdrawals from Ambien more easily though.