Your trip dates, turned into the mornings you need to be awake for. Booking windows are Eastern time; the dates are worked out on your phone.
Reservations open 60 days ahead. If you're staying at a Disney resort hotel you can book your whole stay at once (up to 10 nights) from 60 days before check-in, so one early morning covers every meal. Off property, each date opens on its own morning as it comes into range, so a five-night trip means five early mornings if you want the hard-to-get tables.
That difference is the single most useful thing to know early. It's why an on-property guest booking on day 60 can take the last night's Cinderella's Royal Table before an off-property guest can even see it.
Resort guests book Multi Pass and Single Pass for every day of the stay at once, seven days before check-in. Everyone else books three days before each park day, one day at a time. Single Pass rides sell out first.
On Halloween and Christmas party nights Magic Kingdom closes to regular ticket holders at 6:00pm and the usual fireworks and night parade don't run for them. If a party night lands on your Magic Kingdom day, move the day or buy a party ticket. Nothing else in the trip needs changing.