Computation of time limits in the international phase
If a time limit in any procedure in the international phase starts to run upon issue of a communication, the day of the date of that communication is decisive for computing the end of that time limit, not the date of its receipt. In this respect the PCT differs from the EPC, where the date of receipt of a communication is relevant.
However, if an applicant proves to the satisfaction of the EPO as receiving Office, ISA, SISA or IPEA that the despatch of a communication did not take place on the date that the document bears, the actual date of mailing will be taken as the basis for computing the applicable time limit. Furthermore, if a communication was received more than seven days after the date it bears, the applicable time limit will be extended by the number of days by which the communication was received later than seven days after the date it bears.
Source: http://www.epo.org/applying/international/guide-for-applicants/html/e/ga_c1_10.html
Date retrieved: 17 May 2021