Beta blockers work because they have the abilility to attach to the same receptors in the body that the adrenaline does. Basically they hog the space that the adrenaline would use to give you that nice burst of adrenaline and if the adrenaline can't find a place to attach to, it can't do it's job.
That's why they make hypers feel so much better.
As to missing a dose, it's not a good idea but it probably won't kill you. I have on rare occasions and I'm still here. They do leave your system. If you're enough hyper, your body will probably remind you. You can take them late if you have too. I'd say, don't take them any closer together than 8 to 10 hours if you're using one of the long acting ones. If you have to, move up your next dose and even out the timing by grades until you're back on schedule. If you're on a short acting one, you can probably wait til the next dose without a big problem.
Big thing is, make them a priority, remind yourself with an external clue if you have to. I stick mine on the countertop first thing in the morning and right after supper. I take them twice a day. Once I've taken my dose, I put them where they belong. Doesn't take long for me or my hubby to realize that they're still there when they shouldn't be.
Never abruptly stop taking betas, they need to be tapered slowly so that you're body can slowly adjust to the adrenaline again.
Helen