The 1 April 2021 was on a Thursday, so 52 weeks after will be Thursday 31 March 2022. Clause 42.1 gives your supervisor the power to instruct the contractor to search for a defect until the defects date, which suggests they cannot issue the instruction on the defects date itself. The same applies to notifying a defect under clause 42.2, that too must be notified before the defects date. And, in the case of no defects being notified before the defects date, clause 43.3 requires the supervisor to issue the defects certificate on the defects date.
However, if the supervisor instructed the contractor to search or notify a defect on say the day before the defects date, that is Wednesday 30 March 2022, the defects certificate could not include the defect the contractor has been instructed to search for, because the neither the contractor nor the supervisor will have found it. And even if they did find it on that day, they are too late to notify it.
So, in answer to your question, none of the dates you suggest as a deadline for your supervisor are valid. In practice it needs to be several days before the defects date.