Thanks Iddee, that was the timeframe I was looking for. I figured within some time window they would still identify with eachother, but makes sense that after a few days they would take on their own identity.
Joelel - I'm talking bees in a queenless condition, that have been separated from a hive without the queen and you didn't introduce one (for whatever reason...you wanted them queenless for a cell starter, you wind up short a queen, or queen cell for your splits...whatever).
Take some and put them at the entrance of the other,see if they get attacked,if not they will reunite.
Bees, if separated for a few days, even if from the same hive originally can fight when combined with Joelel's suggestion is impractical. 2-3 days i enough time for a difference to be detected by the bees and bees coming from outside the hive will most probably be attached as being robbers.
Entire frames of bees can often be successfully placed into another since bees on frames belong inside a hive. Placing a brood frame into a hive, in the case of suspected queenlessness, is done frequently and doesn't endanger the nurse bees on the brood frame. Mixing frames of brood and bees from different hives makes a great way to create a strong split without weakening the donor hives and the mixing can be done with out a formal combine. In the case of a known queenless hive, it can be re-queened by taking a frame of brood, nurse bees, and a queen and inserting in into a hive if done within 2-3 days of the hive going queenless.
The tie breaker here is the 2-3 day time period for the odor difference to be a factor or the number of frames being joined. A single frame to a hive can happen anytime, if needed, but within 2-3 days if a queen is involved, because of the time depletion of pheromones. When doing splits by mixing frames from multiple hives it is necessary to tap frames from at least 3 donor hives.