I dumped a bucket of oil off of a small hill and it took a solid 10 minutes to self destroy once the source block was removed. I compared that to lava which self destoryed much fast once I removed the source block.

Also the time between tick seems to leave the oil hanging in the air for a dew ticks when it hits a drop. It creates the overhang then a few ticks later it drops the overhang and sits on the lower block.