How should HR configure the employee’s work schedule so that the morning ("1st Period") and afternoon ("2nd Period") are not given equal weighting for an absence on that day?

In the example where the employee works 8 hours every day, with a 40 hour work week, consisting of 2 hours every morning and 6 hours every afternoon, HR could weight the morning ("1st Period") as 25% and the afternoon ("2nd Period") as 75%. For a 42.5 hour week, consisting of 2.5 hours every morning and 6 hours every afternoon, they could weight the morning ("1st Period") as 29.4% and the afternoon ("2nd Period") as 70.6%.