Opening a bottle of sloe gin?

No - you don't have to let it set. What you are referring to is allowing wine to breathe - or more specifically you are getting it to start oxidizing. It helps open up the flavors in the wine.

Usually the only wines you need to do that with are reds and whites with a lot of tannin in them or that have been oaked.

But for spirits like sloe gin, you don't have to do this - it won't change anything and you'll just be wasting time when you could be drinking :)

yeah, just like other have said its only really meant for wine, and should be decanted (poured into something else rather than left in the bottle)

as for sloe gin, not at all.

only wine needs to breathe..spirits and liquers are open drink and close bottle...sloe gin is delish so enjoy

no, this is generally only done on aged drinks, like spirits and wines

some wines (reds usually) improve and become more complex when you let them breathe a little before drinking

brandy(cognac) and some whiskey is similar

since gins aren't aged, it won't improve letting it breathe.

No it's not necessary, I'm intrigued as to which drinks require 'sitting' for half an hour before drinking.