how long after an enema should my dog pass whats stuck in his rectum?

my dog was constipated for 36 hours i took him to the vets yesterday they gave him an enema and an injection to deflate his prostrate as this was enlarged and blocking the rectum he passed a hard ball but the vet said there was still some in there and to take him home over night and give him liquid parafin which i have but he is still straining and hasnt passed anything shoul i take him back today or leave it a bit longer to see if he goes?/

take him back to the vet today,he is what Dr's called impacted.the vet may give him another enema,and it may help.if the poop is very dry,it has to be removed "manually":leave this for the vet.He/she will put on gloves,some lubricant and remove the hard pieces of poop.consider castrating the dog,as the prostate gets enlarged from testosterone.this will happen again.(very likely)

Within a few hours (at worst!) of the enema!