I think it should be about the same as heroin (length of withdrawal) which is about a week...

Synthetic opiates prevent withdrawal symptoms in the short term. However, once decreasing or ending the synthetic opiate she will go through withdrawal from that, which is often longer than the original drug! However, done with the care of a doctor, can be safe...

It just depends on the half-life... I have been on heroin and prescribed two different synthetic opiates...