Out of time means the cylinder is not rotating exactly in sync with the trigger pull and the barrel.The lockwork is off.In other words the hole in the cylinder is not lining up exactly with the hole in the barrel.In some cases your gun will spit shaved pieces of lead to the rear.Which can suck for any one standing behind you.
I'm not sure if there is a spring which can be adjusted or if there is wear on the rear of the cylinder which might would make a cylinder replacement needed.In some cases it might be more cost effective to simply retire the gun.
What model are we talking about here?I've heard of it happening in low end and top end guns.