Note that [%c_date%] always shows the current date at the moment the page is being viewed, regardless of the buyer's original order date, so you would actually want to use [%p_date%] for the buyer's payment date.
You would need to have some custom javascript written that would take the value of [%p_date%], add 2 or 5 days to it, and insert the result inside the relevant SPANs. The substitution of template variables happens before we send the page to the browser, so your javascript can be written with the presumption that by the time the buyer's browser runs that script, the string [%p_date%] will already be replaced with an actual date (e.g., January 1, 2009).
Consult the Developer Directory link at the very top of this page if you'd like to hire an E-junkie-experienced developer to program that custom javascript for you.
