When you are working from mobile then you can use Facebook pages manager to schedule the post. To know about steps to from mobile then open your app and choose your publish button. Here, write the status and add the media or links, or choose to continue. After that, click on when will this be published? From here, you need to choose the schedule later option. Click on blue check mark and then you need to scroll through menu and choose date and time for post to go live. Choose to done and click to schedule to finish the process.