For background: Property Occupations Act s108 says the appointment for an exclusive agency must state in writing the day the appointment ends. Section 103 says the term of appointment is up to a maximum of 90 days. The Form 6 stipulates a start date and an end date.
Generally, contract terms start at the 'beginning' of the start date and finalise at the 'end' of the end date - so the start date and end date are included in the term.
Including 7/10/20, 4/1/21 is the 90th day - so it would appear the exclusive appointment finalises at the end of 4 January (i.e. it includes 4 January 2021).