Silly question for all you people who always/regularly sleep through the night to avoid dealing with hostiles: why not just play on peaceful?
My observations so far after ~12 minecraft days out in the open since i updated my test world to 18w07c (no idea when i last slept - i generally only sleep to re-set spawn after travelling or before setting off on a Dangerous Expedition or whatever - but i'm sure it's been many, many days):
o updating an existing world to a world with phantoms re-sets the insomnia counter, so you shouldn't be attacked for the first few nights after you update
o killing phantoms seems to reset the counter; my first phantom attack was 5-6 nights after i updated (and set sail looking for new oceans), the second was 5-ish nights after that
o keep your sound up - they do make a scary pterodactyl-swooping-out-of-the-sky-to-attack kind of sound when dive-bombing you. they can be hard to see, especially on a moon-less rainy night, so when you hear them start running and scan the signs for movement...
o you *will* get knocked off your dirt pillar/floating platform if that's how you choose to wait out the night. I'm not sure if they don't spawn at all or just don't attack you if there's a roof over your head; i may build a little shelter to test that out, or i may just wait until i get back home (i'm currently camped on a little island in the middle of the ocean, waiting for some turtle eggs to hatch)
o they do hit kind of hard - keep an eye on your hunger, and don't wander out in the middle of the night if you're not wearing decent armor! bows (and i guess tridents, although i don't have one yet) are more effective than swords/axes.
I won't say that the phantom won't have any effect on how I play - certainly, I'll have to think about the way I do things like night farming/gardening/fishing around my houses and villages, and i'll keep my bow wielded on over-night ocean voyages, and if i'm going to be staying in one spot overnight out in the open i'll dig a hobbit-hole or build a quick little shelter rather than pillaring up to a little floating platform - but I'm certainly not going to start sleeping through the night and missing all the fun!