Workflow

I am new to this system.....I have set up a workflow but it doesn't seem to work, can anyone help?

What I want to happen is when I add a contact into the Leads module it sends that contact an email, then automatically after 4 days it sends another email to that contact, then after another 4 days it sends another email.

I have set up the following workflow:
2. Execute on - when record is created in workflow.
3. Rule Criteria - Created time is today.
4. Actions - send alerts (email).
5. time based action - executes 4 day after rule trigger date - send alert (email. Then another time based action after this - executes 8 days after rule trigger date - send alert (email).

However, I got the first email but the second hasn't come through, is this workflow incorrect?