If the dog has pulled a muscle the dogs pulled muscle should heal on it's own within 2 to 3 days and the dog should be feeling better.
If the dog is still hurting after a few days then the dogs pulled muscle may not be healing properly or the pulled muscle is worse than it seems.
In that case you might want to take the dog to the vet to make sure nothing more serious has happened to the dog other than a pulled muscle.
The last time my dog had a pulled muscle it took 3 days for it to heal.
I called the vet and they said that if the pulled muscle didn't heal within 3 to 4 days to bring the dog into the vet and have him checked out.
But luckily the dog did heal.
Just make sure the dog gets rest and doesn't injure itself anymore.