Do you want to schedule your posts on Mastodon so that you write them now and they are automatically published later?
Some third party apps including Tusky and Fedilab have a built-in scheduling option. Fedilab also runs a website at https://plan.fedilab.app which lets you schedule posts.
If you want a professional scheduled post management system, there are third party commercial services such as https://publer.io and https://buffer.com that now include Mastodon compatibility.
@feditips though I get the convenience of automated scheduled posts, I enjoy it here precisely because if you see a recent post you can reply with the knowledge the poster is probably there to see it. If this place turns into autopost central it will lose all charm for me. Like facebook and instagram have.
It's not quite the same situation, because instagram, facebook etc don't use chronological timelines.
Scheduling posts on Fedi is more about reaching people who are awake when you are asleep etc.