I agree 100% with the answers above.
Additionally, I leave a 6' length of cable between each LNB and the next device (in my case, that'd be a grounding block).
That gives me a place to connect a meter or other equipment for alignment.
It's also a far more convenient place to connect/disconnect the LNB, than right AT the LNB!
While I put big expensive switches inside, I do sometimes put little cheap ones outside.
Most are not rated for outdoor use - check their documentation.
Weather here is very mild, with minimal rain. So, I put 'em under the eaves, out of light and rain.
Cables should also have a "drip loop" in them wherever the connect to 'the next device", another reason for a few extra feet.
That is a loop or wiggle in the cable to make sure any water flowing down the cable falls off it before the cable turns upward to plug into the motor/switch/block, etc.
And, it's useful to use tie wraps to restrain cables, but do not tighten them enough to make indentions in your cable.
Also, I've found that too many tie wraps, used to make an install look too neat, almost invariably cause a problem next time you work on your equipment.
So, use just a few at strategic locations, and leave 'em a little slack.
edit: to more properly address the question of 6" cables to a switch...
I assume you want to put the switch right out on the arm under two LNBs?
Please consider putting it on the back of the dish, where it will have at least minimal protection.