based on my experience the online system adds an extra day.
eg. last online I submitted was on 28-Feb-2023 at 07:53. it was approved same day with next report due on 29-May-2023, not 28-May as expected.
I can no longer do reports online and last in-person report was done on 05-Sep-2023 with next due date of 03-Dec-2023, as expected.