how do i set wait condition as to send a mail before 10 days of due date

Hi,

I am unable to make a workflow for the following condion:

An email shoud be sent to owner of task, if only ten days are left in due date.

i.e.  today's date should be equal to due date -10 days.

Need to know the syntax to be written in wait condition and also what must be written in evaluation condition.

Thanks in advance for help.