Well it depends highly on your definition of slavery. I can't tell you how quickly the slaveowners adjusted their behavior, but I can tell you that once they had adjusted, things were extremely similar to how they were before.

When the war ended, blacks were led to believe that they would be compensated in some way for the work they did as slaves. General Sherman made a promise that each family would get "40 acres and a mule," this land coming mostly from Georgia. This ended up not being fulfilled very well. There was a lot of unclaimed land that had been granted to blacks, but after the war ended, Andrew Johnson quite rapidly granted all land back to its original landowners, meaning blacks would either have to be evicted or agree to bind themselves to the landowners and work the land in exchange for food and lodging. This system of labor, sharecropping, developed because the workers and the landowners still needed each other, and union reconstruction efforts were somewhat feeble. Sharecropping ended up looking a lot like slavery.

This, in conjunction with coordinated efforts to stop blacks from voting, meant that the conditions of blacks were not very different from how they had been before. In some ways, it was worse, because to the landowners, blacks were now expendable, as opposed to being property. This opened things up to considerable abuse. The most important difference I can think of between sharecropping and slavery is that eventually poor whites began to till the land as well, alongside former slaves.

With these facts in mind, I had a US history teacher in high school tell me that the earliest slavery could be truly considered gone was 100 years after it was abolished, when the civil rights act passed. Some food for thought.

If I got anything wrong, please correct me. I'm running off of memory here (mobile, poor connection).