I'm 71 yrs young. I managed to walk 16 miles in 2 1/2 days. If i did not stop to look at shops and exhibits, I would be able to walk a park in 1 day. I'm thinking weekends and holidays are the busiest days.
We were there this past saturday and it was pretty shoulder to shoulder busy.
Weekends are probably the busiest, but you should check a site with a crowd calendar like touringplans.com
Weekends are busiest it's hard to get round in a day
Animal kingdom absolutely can be done in one day. During the summer time it's always busy but it's not as bad as magic kingdom in my opinion. We were there during the middle of the week.
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