Schedule a follow-up task (email sending) after 30 days.

Hi there,
We are trying to set up a diary study, consisting of a pre-diary survey followed by 10 short diary surveys. Each of the short diary surveys are scheduled to take place every second day, with the first one being sent out 3 weeks after the prediary survey. This means that after the 5th diary survey, we need to schedule the action (send the email) in a period that goes beyond the 30-days option. As far as I can see there is no option that one can use to flexibly arrange sending an email after, say 40 days. Is there anything that we can do about it?
Thanks in advance