2.1.664 Part 1 Section 18.3.2.4, dateGroupItem (Date Grouping)

a.   The standard does not specify a default value for the month attribute.

Excel uses a default value of 1 for this attribute.

b.   The standard does not specify a default value for the day attribute.

Excel uses a default value of 1 for this attribute.

c.   The standard does not specify a default value for the hour attribute.

Excel uses a default value of 0 for this attribute.

d.   The standard does not specify a default value for the minute attribute.

Excel uses a default value of 0 for this attribute.

e.   The standard does not specify a default value for the second attribute.

Excel uses a default value of 0 for this attribute.