Do you mean how long
until the drug can no longer be detected in your system, or how long
will withdrawals last after you stop taking them?
Hydrocodone has a half life of about 4 hours. (That means half as much will still be in your blood stream 4 hours after your last dose...then half THAT in another 4 hours, and so on.)
In terms of withdrawals, however, it depends on how long you've been taking them, your average daily intake, etc.