To check if VirusScan is up to date go to the Start button, select Programs, and choose McAfee, then VirusScan Console. When this has started, in the menu click on Help then About.... This will display a dialogue box which has the scan engine version and virus definitions number and release date.
If your system is on the Managed ePO service, you can check your dat version by right-clicking the 'M' shield in the system tray, selecting About... and scrolling down the list of information.
http://www.mcafee.com/apps/downloads/security-updates/security-updates.aspx shows the latest dat version available
The virus definitions are normally incremented on a daily basis, normally in the early evening (GMT) our time.