Do you mean in the web console for version 4.0?
The sorting only works on dates without the time information attached and only for a defined list of names:
"lastseen", "last scanned", "last changed", "last seen","lastchanged", "lastscanned","purchasedate", "warrantydate", "warranty date", "purchase date", "lastpatched","lastfullbackup","lastfullimage", "warranty expiration"