Are the requirements for the mission day the same as 2nd sunday (any six missions between 0:00 and 23:59)?
Nope, mission days are special sets of missions, in selected locations,
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A formal mission day consists of 18 curated missions, during which you must complete any 6 of those as a minimum, then check in with the organizers to show your completion at the end party.
At the latest Mission Day in Jacksonville, the official missions could be completed any time between 0:00 and 23:59 that day to get credit. Badge tick was automatic upon completing the sixth mission. No check in was required.