Why is the Change of Grading Basis deadline the Eleventh Monday for Spring 2021?

The original Change of Grading Basis deadline is typically the Fifth Monday of term. Due to COVID-19, Harvard College updated the Change of Grading Basis deadline in the Student Handbook on December 8, 2020

For Spring 2021, the deadline to change the grading status of a course will be extended to Monday, April 5, or the Eleventh Monday of the semester. Students will continue to be required to complete 84 satisfactory letter-graded credits for their degree, and first-year students and sophomores will continue to be expected to take three letter-graded courses per semester.