what period of celibacy would make a difference in rebuilding the ojas for someone who had a draining lifestyle for some time? (i know nothing about rasayana but will try to imporve my diet).
how long breaks between sexual intercourses are advisable for maintaining good health? is it the general rule - the less sex the better?
Yes -- here is a general guideline for men. Though this has changed a bit with modern diet and availability of foods around the seasons from all over the world, there are still some trends we can observe -- when it is hot, we tend to eat much lighter and lighter, less nutritious food, and when it is cold, we eat heavier, oilier, more nutritious food. When people ate according to the cycle of the year, this was much more pronounced. Therefore, in the winter months, when it is cold and one is eating a lot of heavy food, one can ejaculate as much as five times a day with no health problem. As one moves through spring, this reduces to every two days, and finally in summer only every two weeks. When one starts to increase one's intake of nutritious foods in the fall through harvest and slaughter season (which happens in late fall in Tibet), then one can increase to every other day.
Now, if someone is depleted, they should not have sex because in this case, as in summer, one loses a little ojas with ejaculation. If one is healthy, winter time, eating well, etc., there is no danger of losing ojas because one has excess.
While women do not have the same issue -- menstruation can be a cause of depleting ojas if they are not careful with their diet.
Ojas is mainly depleted by stress. A lot of autoimmune disorders come from depleted ojas because of modern lifestyle.