Approval is valid for the requested duration of the project listed by the researcher on the proposal form up until one year.  For projects lasting more than 1 year, the researchers must submit a Continuing Review Form within a month prior to the expiration of the approved year.  (see (4) in http://www.hhs.gov/ohrp/humansubjects/guidance/45cfr46.html#46.103 and (e) of http://www.hhs.gov/ohrp/humansubjects/guidance/45cfr46.html#46.109).  If the IRB questions the duration period, the researcher may be asked to revise the timeline. If the researcher finds that an extension of the approval period is needed, the researcher may submit a Continuing Revew form requesting the extension along with an explanation for the need. Most extensions are granted; the concern of the IRB is that projects above minimal risk are justified to continue or that mimimal risk studies are not wasting resources.