When exporting data to email, you have the ability to edit the email subject according to your preferences. 

You are also able to add the dynamic order number and date time to the email subject.

Add order number on email with the placeholder {{source.first_order_number}}. The placeholder can be added in between any words. 

You can also add the date time to the email subject by pasting this code in the Email subject field.

{{'now' | in_time_zone: source.timezone | date: source.datetime_format }}

You can choose to add before, after, or in between the subject by placing the code accordingly.

The date-time format follows the file date format.