This property specifies the end of the validity of the Offering.
A time-zone should be specified. For a time in GMT/UTC, simply add a "Z" following the time:
2008-05-30T09:30:10Z.
Alternatively, you can specify an offset from the UTC time by adding a positive or negative time following the time:
2008-05-30T09:30:10-09:00
or
2008-05-30T09:30:10+09:00.