Short Answer:
This depends on your metabolism, but in general it will stay in your system for 24-36 hours with a *low dose* (ie. no more than 30mg of codein). However with larger doses, it will be in your system for 48-72 hours depending on how high your dosage was.
Long Answer:
The half-life of codeine is 2.9 hours. This means that in 2.9 hours, only half the amount of codeine is remaining. In another 2.9 hours another half of that, and so on. However you must keep in mind that codeine is a prodrug. It's main metabolite is Morphine. Some of these metabolites can remain in your system in low traces, for upto 72 hours. It all depends on your dosage.
Call your pharmacist and ask...they should know.