Plan Checks are good for 6 months or 180 days. If you will be going passed the 6 month period, you will still be eligible for (2) - 90 day extensions ($82 each extension). (Municipal Code Section 15.18.050. Subsection 105.3.2)
Plan checks for development projects where permits have expired for a period of less than one year shall be assessed a fee equal to half of the amount of the applicable plan check fee, as set forth in the resolution establishing said fee, if the plans that are being resubmitted are identical to the prior plans. Said fee shall be paid when the plans are re-submitted for review by the building official.
105.5 Expiration. Every permit issued by the building official under the provisions of the technical codes shall expire by limitation and become null and void, if the building or work authorized by such permit is not completed through final inspection within the allowed time from the date of issuance of such permit, which time shall be as follows: up to 5,000 square feet, 18 months; 5,000 to 10,000 square feet, 24 months; over 10,000 square feet, 30 months. For good cause, upon initial application for a permit, the building official may establish a different expiration date when it is anticipated such date will be necessary to complete construction due to extenuating circumstances. Upon expiration, before work under the permit can be recommenced, a new permit shall be obtained. Such new permit shall be valid for 24 months, and the fee therefore shall be one half the amount required for a new permit for such work, if no changes have been made or will be made in the original plans and specifications for the work and not more than one year has passed since the expiration of the permit; otherwise, such new permit shall be subject to all terms and conditions applicable to new permits.