TimeTap provides you with a couple marketing an invitation templates upon your account creation (the "Blank Template" and the "New Client Welcome Message") and you can add your own templates as well.
...
Step 1: Go to Messaging > Marketing Invitation Templates:
Step 2: Click the "View" button next to the template you'd like to edit:
Step 3: Click the "Edit" button next to the "Template" section on the template profile:
Step 4: Make the changes you'd like to make to the template and then press "Save":
Now when I go to email my clients template, if I select that template I will see those changes reflected: