Times are not necessarily accurate. Last month, I went several times on several days when the app said Chip & Dale would be at the challenge trail and they were never there.
Characters with specific times in the app are generally there during those times but those with a larger block of time should be treated like: "there's a chance that this character will appear here sometime today within that time window". Of course, there's also other roaming characters whose times are not listed in the app.