I would put them up, just not light them up, if they are obviously for Christmas.
Many people with elaborate designs leave some of the lights strung up all year. Even should a lighting design be just the garden variety & you're my DSis & BIL, you leave them up all year 'round!
If I needed assistance & the help was there, I'd make hay while the sun shined, just not turn on the lights.
It's true, as another poster observed, they could be Halloween lights.
I must admit I gave thought today of asking DH to put up our window wreathes!

Just because it is a nice day & late November could be ice & snow & he needs to be on the extension ladder up 2 stories.
I really don't like the early decorations in the stores.
they are not there to give us a religious feeling, just to encourage mega spending. For me, seeing Christmas decorations before Thanksgiving--& seeing them out now!--just makes me astonished by the greed. but that's me & I'm the 1st to say I have a real Puritan streak!

I can see how some would think they're pretty even in September!
Jean