Try about a week or two before your trip
Like my brother from another mother Brad said; the postings are only two weeks ahead. The showings do not sell out very fast unless it is a much anticipated new release. In that case go online two weeks before your trip and book the showing you want. Do not sit close, sit further back past the middle row.
You just have to keep checking as you get closer to the date.
Usually they only show about 2 weeks out unless it's a big event like Endgame.
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