The self-lodgement tax deadline falls on 31 October every year, closing the four-month window that opened on 1 July. 3 October 2029 falls inside October, the final month of that window, in the fourth calendar quarter of 2029, with the deadline drawing closer as the month progresses.
A public holiday landing on a Wednesday sits in the middle of its working week rather than beside a weekend, so it does not create a long weekend on its own. Wednesday 3 October 2029 falls on this day of the week, at the working week's midpoint, three working days deep into the week.
2029 has 365 days on the calendar. Leap years add a single extra day to February, giving those years 366 days instead of 365 and shifting the day-of-year number for every date from March onward by one compared with an ordinary year. This is the only irregularity in the length of the Australian calendar year.