[Ravenseye]

That's plenty of room. Sometimes when I get a few nucs or do splits I end up with more hives that I planned for and they sit side by each without a problem. I think you'll be fine.

 

[little_john]

In my view, it's not the distance between hives which is important, but rather the distance between entrances. So - nuc boxes with a single, central hole can be placed physically closer, than (say) brood boxes with wide slots. The sub-species of bee is also a factor, with Italians being more prone to drifting than Carnies.

With full-width slots, I'd go for 18", with single, central holes 12" - both within your spec.

If you can point the entrances in different directions, then place the boxes as close as you like ...
LJ

 

[enjambres]

My telecovers often touch each other, so that's about as close as you can get. But for easy of working I prefer more butt-room b between the hives. I doubt the bees care much. In Europe, it's not uncommon for some hive setups to share common walls on a specially-built trailer.

All my entrances face the same way, BTW, whether centered or reduced with the reducer in place.

Sometimes I speculate that my unusually calm yard benefits, collectively, from appearing to strangers outside the yard as being a single really, really, big colony not worth messin' with just to steal a bit of honey. I have mixed-sizes of hives within the yard (from a nuc, to three-deep wintered-over Big Girls) though. I also protect most entrances nearly all the time with robbing screens, which are identical in design. A quiet. unfussed, "happy" yard is one of my main goals.

Nancy

 

[ericweller]

My benches hold 4 hives and I place each hive facing in a different direction. I think this works very well to prevent drifting. There is about 5 inches between hives.

 

[Michael Bush]

My hives are all touching both side to side and back to back...