Generally, when you want to modify the information of an ad that is already published in the Contractor Profile, you need to make an amendment.
This rule, however, has an exception: it is not necessary to make an amendment when it comes to modifying the date of opening of envelopes of a file that has enabled the submission of proposals through Digital Envelope. In this case, to change the envelope opening date, simply go to Digital Envelope Management, change the date, and save the change. Once done, an amendment will be automatically published in the Contractor's Profile informing the new opening date, and with the reason for the amendment: "opening of envelopes".
You will find it explained in the FAQ Modify the envelope opening date available at PSCP Support Portal.