Mastodon's timeline API is paginated with a `max_id` param which is the id of the last status you got.

https://docs.joinmastodon.org/methods/timelines/#query-parameters-1

If I'm fetching multiple timelines, and the user clicks "next" I need to keep track of the last id I got from each account, and fetch the max_id I got from each one.

This was simpler when I was only querying for one account.