Only group administrators have the possibility to schedule posts in advance and adapt them to their individual time management.
First create a post in the specific group by clicking on the "+ Post" button at the bottom right. Then design your headline and post content and feel free to add files. How to create posts can be read again in the following article: How do I create a post?
To schedule this post, click on the "Schedule" button above the headline and then select the date and time. Once you have entered this information, click on the "Schedule" button in the upper right corner. Your post is now created and will be published on the planned date in the selected group.
Already planned posts, which are not yet published, can be found in the news area by using the button "Scheduled posts". These can be edited again if necessary.