I'm drawing my answer from How To Grow Native Plants of Texas and the Southwest by Jill Nokes which says: sugar maple cuttings are best taken in late spring after the first stage of shoot elongation has ended. Thick cuttings, four to six inches , taken from terminal or lateral twigs in summer root best. Treat with high concentrations of IBA (indole-3-butyric acid) and keep under intermittent mist. [Yes, the text mentions both late spring and summer. I'm guessing that means cuttings can be taken for up to 2 months.] Plant rooted cuttings in individual containers, and place in a cold frame over winter. Soaking sugar maple cuttings in IBA at the rate of 50mg/liter for 3 hours before planting improved rooting in one study.

The author only mentions the IBA hormone, not any specific brand. However, Hormex only seems to sell one higher concentration. Their #16 is twice as strong as #8 (1.60% vs 0.80%). I think your #8 should be sufficient. It can take up to 3 months for cuttings to root.

Interestingly, another source (Dirr and Heuser, "The Reference Manual of Woody Plant Propagation") indicates that rooting hormone did not help this species root, and in at least one case cuttings without hormone rooted better than those that received it.

Illstep (6a) interesting. Do you have link to the thing talking about rooting better without hormone? Thanks.

It's a book, so no. Title and authors were in my previous post if you're interested - but I should mention that it doesn't go into much more detail than I already provided.

Thanks guys.