Depending on how long you have had both, a proper 2 weeks apart would be best before putting them in the same tank :) What I do it set the tank up, fill like I am doing a 100% water change on their old tanks, let them float in their cups to make sure it's the same temp (for about 15mins) and then put them in their space of the tank. I don't get them used to the water chemistry because it's the same as it's always been, just clean.
thank you very much Pitluvs. the VT is a bit more agressive but he even bit his tail in the 2.5g, the DT is shyier and has no serious biting issues in the 2.5g. how much tail damage is acceptable for them to get used to the divided 5gal? atm the VT is a special case where he seems to like the .5g, i will still try him out in the 5gal bc .5g is a bit annoying to keep a betta in .5g.
regarding the DIY divider supplies do other stores keep the plastic binders than staples? the one nearby (Bureau en Gros) has only the binders with report sheets. i got them anyway for $6.50.
is that a half gallon kritter keeper? also hope ur using the energy efficiant bulbs incedenent or how ev its spelled MELT the plastic. i had mine like 5in away n the like 30watt inc. started melting and deforming it :) just a heads up ^.^