Are the Amounts on a T4 from a fiscal year or do they have to be from the calendar/tax year only?

Are the Amounts on a T4 allowed to be from a fiscal year or do they have to be from the calendar/tax year only?

Example:

If a company pays it's employees on a bi-weekly schedule, can they use the amounts from the 26th/last pay stub to enter onto T4?

Getting started

Your T4 should be amounts received from January 1, 2017 to December 31, 2017.