You also may be better off with regular Ambien, not the CR's. I'm not sure if you'll get a lot of recreational effects from the extended release versions but I could be wrong. It seems you'd just have to take more of them at once to get the same effects you could get with the IRs. Plus the IRs are generic... = cheap.
But for opiate withdrawal relief I could definitely see the CR's being more beneficial. The CR's are 12.5 mg no? I'd take at bare minimum two of those to get opiate relief; ut you may have to go higher up than that just because of the extended release business. With regular IR Ambien I'd suggest 20mg minimum, so with the CR 25mg (2x 12.5) initially you won't feel much but it will build over time and help you relax even though it may not knock you out.
IF you want to be knocked out, then you'd have to up the dosage a bit more; maybe take 4 of them so 4 x 12.5 = 50 mg... should hopefully let you sleep but ti depends on how bad your WDs are.