Do you want to schedule your posts on Mastodon? There are many options you can use to do this.

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.