Updating Profile Time Zone

I'm looking to create a workflow that will allow us to update a profiles time zone based there province/state.  All of are members are currently set to the default time zone which prevents us from being able to get use of the "Sending messages at the recipient's time zone" function on an email delivery.  I would like to create a work that can update this profile field for me.  I'm just not sure exactly on the expression needed on the update.  Would appreciate any help on what others have done?