Hello BO, hope you are well.
A full clean (filters & water) on the entire house.
One good days labor. (With overtime) so 8-12hours.
Water changes only on the entire house, 2-3 hours if the going is good!
(That's 24 litres exchange on four systems and 170 litres on one)
266 litre or 70US Gal.
Normally this is divided into a morning session and an afternoon or evening session.
I do this every Sunday almost without fail.
More recently I've been splitting up the filters so it happens over the course of the week rather than all on one day. The going is a bit easier!
My biggest system is the only headache, 50% changes occur in two halves.
(Water out/half return day one, second stage refill on day two)
Water production time is the problem, I'm keen enough!
Also there are daily/mid week sessions which are generally much shorter unless Sunday goes wayward, in this case Monday is a busy time!
I have no fancy exchange method it's all done the old fashioned way, water in a bucket. Fortunately everything is within arms reach of the sink!
FISH HOUSE JOY