What is the value that you are currently inserting into the date column on your confirm page? You will need to ensure that the value you are inserting contains a properly formatted timestamp. When you say 'timestamp' are you referring to a unix style time stamp that is a integer value for the number of seconds or are you talking about a MySQL style timestamp field?
Regardless, you will need to ensure that the value you are inserting has a valid timestamp for the type of column you are inserting into. If you have no value currently setup like this the easiest thing to do would be to add in a session variable that has a value of the current time. You would then reference this session variable in the server behavior for the value of your date column.