The device must be rooted to monitor Whatsapp, Facebook and Viber messages. It is limitation of android system.
Scheduled Screenshots is available for rooted devices in the version above 3.3.207.
How to root: please use refer to this site: http://www.xda-developers.com/root/
Then restart the phone. Sign into the program on the phone. Will be offered to permission, select agree. If necessary, reboot the phone.