Are you importing the frames as a sequence? That's where you start.
Yes, I go File, Import, File...then when I select the first picture it automatically selects jpeg sequence at the bottom. When I hit enter it puts it in order then I can drag to the timeline as a sequence.
Make sure the sequence is interpreted at the same frame rate as the comp. Your problem is probably a frame rate mismatch.
suggest you spend a few hours cruising
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