Officialy Facebook now give the option to pre schedule updates for page admins. Now page administrator's can schedule posts in advance up to next 6 months, adding feature that were previously only available in third party apps. With help of below multi-step process you can schedule your updates.
How to Pre-Schedule Your Status Update
1. At first log-in to your Facebook fan page and click inside your page's status update area,
2. Now click on small grey clock icon will appear in the lower left-hand corner.
3. Now click "Add Year" link from within the dropdown menu, select the year in which you want to post the update,
4. Then click "Add Month" and select the month you want to update to go live,
5. Now click "Add Day" and enter the date,
6. Now click on "Add Hour" and then "Add minute" of the day to post
7. Finally click on "schedule"
7. Finally click on "schedule"
Once Facebook saves your update, you’ll see this popup box,
How to see or reschedule your scheduled post
To see or reschedule your scheduled posts, scroll up to the top of your page and click "Edit Page > Use Activity Log"
Now your scheduled posts will display.
Here you can either change the time, publish your post immediately, or cancel it altogether. Enjoy :)
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