I depends on light and temperature. IMO.
Mine put out a new leaf every 3-4 weeks while in direct sun in a southern window, but now in an west facing window with lower temps, no new leaf in past 8 weeks. I am actually happy for that because the summer growth is nice healthy and compact. I don't want an etiolated section on that branch.
Surprisingly my Ficus elastica 'Tineke' that sits on the same windowsill has unfurled a leaf the other day.

The rate of growth, and by extension the rate at which new leaves appear depends on where the plant is in it's growth cycle (what time of year it is) and the severity of the limitations imposed by cultural conditions. IOW, large plant "A", during the summer and growing under perfect conditions might make 20 leaves/wk, while the same size plant "B" growing under deplorable conditions might not only produce NO new foliage, it might even shed some of the existing leaves.

The question can only be qualified; there really is no answer.

Al

Haha well, mine is rather a cutting than a tree at this stage of his life.
I am happy with it, bought it in late June, transplanted to semi-hydro. It adjusted quickly and never shed a leaf. I wish it was a tree with 20 new leaves :)

here is a pic of one of mine

Green fingers . Looks great