ow long is a piece of string, sorry to say.
I import LOTS of firearms, and the restrictions on those are MUCH harsher (including doing safety testing etc) than astronomy items
. I have had some clear in a week, yet some may take a month or more (Sydney Customs is MUCH more "effective" than others, yet Brisbane is quite painless).
So, as the old saying goes, Hurry Up (do your paperwork etc) and wait.