Half life for Durabolin (Nandrolone Phenylpropionate) = 1 day
Durabolin is just a derivative of the famous Deca, although it's very similar it's much faster acting and therefore gets into the system quicker than Deca, but leaves the system quicker also.
Deca's half life = 6 days
This is one of the reasons why Deca is more popular than Durabolin. Some say that Durabolin is safer but less effective than Deca.
They're both very good bodybuilding drugs, you just have to adjust dosing frequency depending on which one you're using.