An applicant can request a SIS up to the end of 22 months from the priority date. The request must be filed with the IB.
GL/ISPE 2.20, 15.78
PCT Newsletter 10/2016, 1
The SISA must start the search promptly after receipt of the necessary documents, though it may delay the start of the search until it has received the ISR from the main ISA, but not later than the end of 22 months from the priority date.
The supplementary international search report (SISR) must be established within 28 months from the priority date so as to allow the applicant to take it into account when deciding whether or not to enter the regional/national phase.
The file will therefore be sent to the examiner as soon as all the documents have been received, including the ISR from the main ISA. If, however, the ISR from the main ISA is not received within 22 months of the priority date, the file will be sent to the examiner to enable the start of the search.