Importing time series data using Time Series Tools - Custom date format

Hi I want to import time series data using the time series tools GUI

My time/date is in the format dd/mm/yyyy HH:MM:ss (all one column) eg: 15/10/2012 14:03:00 = 15th October

This format isn't listed under the 'format' drop down menu so I want to use the 'custom' option - however, selecting 'custom' does not enable one to enter a custom format.

Can some one please explain how to do so?

Many Thanks, Ant.