The suggestion is to wait 90 minutes
after exercise before offering the breast.

Don't bother. Feed the kid ad lib and watch for reactions. These women
exercised to the maximum (not advised) as a scientific study. It's
irrelevant to normal exercise and I seem to remember small sample size as
well. If a mother finds this the advice you give is to put more energy into
other things and less into exercise and baby and she will both benefit.
Maureen