I've seen very contradictory info about this hermya (and am just about to add my own here, sorry).
I started expressing and feeding one bottle feed at 10 days. It was fine, and caused us no problems at all. It was a very big help for me to be able to get a break for one feed.
My MW talked about the 'before 6 week window' of opportunity for introducing a bottle (and I'm glad she did, as all I'd heard before that was 'don't do it until several months in, when BF is 'well established' - but there have been quite a few threads on here from mums whose older babies are bottle refusniks, when they are desperate for them to take one or two as they need to go back to work...)
Anyway - the MW said that nipple confusion wasn't likely to arise for a baby feeding well and happily with a good latch, if you were giving one bottle a day. For babies who weren't feeding easily on the breast then it could cause problems, as they don't have to work as hard to get milk from the bottle, and might start fussing or refusing the breast.
MW also said that offering the bottle once a day was a good idea, so they didn't forget how to do it. She warned against trying it once, thinking 'oh, baby can do that fine' and then not trying again for a couple of months, as they won't remember what to do.
As far going a long time without offering a feed from breasts.... well, I guess it depends a bit how often your DC feeds, and whether your supply is okay atm. Even skipping a feed meant I never got to go 'quite a long time' between feeds!
I was advised to pump a little bit at the start and end of each feed, and not to 'go crazy' as it might suddenly send my supply rocketing, and give me engorgement problems. Pumping little and often to start with gave me a couple of ounces to for DP to feed later that evening.
After missing that feed, my boobs were a bit fuller than usual, but frankly DS was feeding so often, I never got to go longer than 3-4 hours without feeding, even if DP gave a bottle feed. If they were very full, I would express a tiny bit before feeding to help DS latch on and make me totally comfy.
So that's my experience. No doubt lots of folk will be along with different experience and advice! I should add that DS never had any latch issues, I never had any supply issues - sometimes he would polish off a bottle of EBM and then switch to breast if he was still peckish. He never had any problems doing that. I think for someone who is having problems BF-ing then the whole 'expressing/bottle feeding' scenario is likely to be harder and might well cause problems.