Since my cataract surgeries replaced my natural lenses with specific prescription intraocular implant lenses, yes - I kept my BG in tight control leading up to it because I didn't want to risk any miscue in the prescriptions of the intraocular lenses. What the time table would be on that, I have not the remotest idea - all I knew was that the minute Medicare kicked in, I wanted that done, so I was being really compulsive about it. But my cataracts preceded my diabetes by many years, so not sure my experience is relevant.
And when my ophthalmologist questioned me about my general health (as he should, you know - he's a regular MD, and needs to be aware of other medical issues too), I admitted I hadn't had any "wellness" tests done for many years, due to lack of insurance. He suggested we postpone the cataract procedures until I'd had the colonoscopy/mammogram/etc/etc., to check for more serious maladies like cancer. I may have stopped him in mid-sentence . . . NOTHING is going to get between me & getting rid of these cataracts! Not diabetes, not cancer, not ANYthing!