In basic syntax, it means your free minutes will last until the 23rd of November. Using midnight as a cut-off point or whatever expiry time was setup on the O2 system. Message notifications are not very clear in some cases and this non-specific gobblegook is the nearest you are going to get to English.
YOU HAVE FREE MINS LEFT UNTIL 23 NOV 2014
Use free minutes until 23 Nov and then they will not be free anymore.