There's a free tool called
Hootsuite that can help you schedule your social media messages (Facebook personal and pages, Linkedin, Ping.fm, Wordpress, Myspace and Foursquare).
You can also set up team members (e.g. your virtual assistant) so that you don't have to give out your user ID and password to others. Simply make them part of your team.
Scheduling your Facebook posts on Hootsuite is easy:
First, connect your Facebook account to Hootsuite
1. Log into hootsuite
2. Go to "settings" (bottom left)
3. Click the Facebook tab
4. Click "Connect with Facebook"
Now, start posting:
1. Type in your message.
2. Select the networks that you want to post your message to (in your case: Facebook)
3. Select the time and date you want your message posted.
That's it.