For GL, it is March to March. Not really sure why, just looked it up in the Const. thinking it might have simply been the first Month a GM was installed. I see our articles of union (bringing lodges from three (EC, SC & IC) Constitutions together are dated Melbourne, 14th January, 1889... but then
Article 1. — That the Masters, Past Masters, and Wardens of Lodges, under the
above Constitutions, having been summoned, attend a meeting on the 20th
day of March next, at the Freemasons’ Hall, Collins Street, Melbourne, and
form themselves into a Grand Lodge to be styled “The United Grand Lodge of
Antient, Free and Accepted Masons of Victoria”, and proceed then and there
to elect some distinguished Brother to be the Grand Master of the said United
Grand Lodge.
Good enough for me - it is March because that's when it started from.
Subordinate Lodges set their month for Installation, normally again from Foundation. If they vary the month installation one year, I've can't think of an example where it was not corrected back or forward to the traditional month hen the lodge was first founded.. but I am sure it has happened.
In the past dues were paid from Installation from Installation. This has been changed recently,it is now 1 July to 30 June which is also the standard financial year here in Australia.