A mixed use approval shall expire and become void unless substantial construction is commenced within two years of the date of approval of the final plan, or within a longer period if specifically authorized in the phasing or construction schedules approved in the final plan and is substantially completed within the approved phasing or construction schedules; provided, such time periods shall be tolled during the pendency of any litigation related to the mixed use project that prevents the applicant from commencing or completing such construction; and further provided, that prior to the expiration of the mixed use approval, an applicant may apply directly to the city council for one or more extensions not to exceed one year each. The city council shall approve such extension or extensions upon a finding of good cause.