I had three bouts of preterm labor, and spent a total of 7 days in the hospital on mag sulfate, and the I was on oral nifedipine until 36 weeks. I went off the nifedipine, and it was three weeks exactly before DD was born. She was born at exactly 39 weeks. I was fully effaced, and 3 cm, from about 31 weeks.
Honestly, I've become a little sceptical about the effectiveness of tocolytic drugs (mag sulfate, terbutaline, nifedipine, etc.). The research I've done seems to indicate that they are only effective in the short-term, like to buy a little time to transfer mom to a larger hospital with an NICU, or to allow for steroid injections for lung maturity. I am pretty convinced that maintenance doses of these drugs, like the nifedipine I took, are pretty useless. If birth is imminent, they will not stop it, and if they seem to "work" it is likely because birth really wasn't imminent.
Anyway, enough of my babbling. My point is basically that the nifedipine leaves your system after about 24 hours, or slightly more, but that does not mean you will necessarily labor and delivery any time soon.
BTW, good luck and best wishes. I hope that your baby's birth, whenever it happens, is a wonderful experience, and that baby is healthy.
me , he , my three , , and -- and the one we lost