Parameters are not flexible enough to do what you need. There are some
horrible workarounds, but they are very inefficient.

The simplest solution is to provide a form where the user can enter the date
range they want to cover. You can then supply all values if they enter no
dates, all values onwards if they just enter the first, all values up to the
second one if they just enter the 2nd, or all values between the dates if
they enter both.

There is an example of how to do that in the 2nd part of this article:
   Limiting a Report to a Date Range
at:
   http://allenbrowne.com/casu-08.html
You can do exactly the same thing as a Filter for a form, or to build the
SQL statement directly in code.