Montgomery GI Bill Degree Extension Act of 2008 - Extends the time limitation (generally ten years from the original eligibility date) for the use of educational assistance under the Montgomery GI Bill all-volunteer force educational assistance program, in the case of an individual who has completed at least 50% of the credit or time requirements leading to a degree or certificate before the last day of the ten-year period, to the earlier of: (1) the date on which the individual completes such requirements; or (2) two years after the last day of the ten-year period.