So there are a couple types of posts in AmebaOwnd, like Wordpress really. In addition to modifying the date of a post after you publish, you can also schedule a post to release at a future date, from both desktop and the mobile app. In the mobile app there called reversed posts (Makes no sense lol) but that’s what they’re called lol.
Create your post, either in its entirety or just a title and a couple words (you’re going to have to fill out both in order to save the post) and then click the date and time field. You then can select a date in the future instead of publishing the post immediately. To complete the post and schedule it, goose schedule from the top right.
Not really a step per se, but I’m just going to show you where to find those scheduled posts. From the main menu of the app in iOS, choose posts and then you’ll find your newly scheduled/ (reserved haha) post in the Reserved section. When the time comes that you’ve specified, your post will be published on your site.