Any food supplementation is a two-edged sword: you want to attain a proper level of a nutrient, without getting too much and causing other problems. Various people absorb iron at different rates. And excessive iron has been implicated in heart problems, so you certainly don't want to overdo it. The NIH recommends iron supplements be taken in two or three fractions per day for optimum delivery.
This US National Institute of Health (NIH)
iron supplementation factsheet has some excellent information you might find helpful.
...Many men and women who engage in regular, intense exercise such as jogging, competitive swimming, and cycling have marginal or inadequate iron status. Possible explanations include increased gastrointestinal blood loss after running and a greater turnover of red blood cells. Also, red blood cells within the foot can rupture while running. For these reasons, the need for iron may be 30% greater in those who engage in regular intense exercise.
Three groups of athletes may be at greatest risk of iron depletion and deficiency: female athletes, distance runners, and vegetarian athletes. It is particularly important for members of these groups to consume recommended amounts of iron and to pay attention to dietary factors that enhance iron absorption....