Athanasius of Alexandria — on 2Tim 4:2 (FESTAL LETTERS 1.1)

“It is our duty and obligation to remember and heed the special day of Easter Sunday every year. St. Paul taught his disciple Timothy to be aware of dates, saying, "Stand ready in season and out of season." Paul wrote that, of course, so that Timothy would do things when they were supposed to be done and avoid the blame for doing things at the wrong time.”