I have broken my middle toe & am a fitness instructor, how long before it is safe to do high impact exercises on it eg: jumping and lunges?

Hold on. It will probably take a minimum of 8 to 10 weeks and i would not be surprised if it would be 12 weeks. Get it immobilized and use ice.
Takes bone. About 6-8 weeks to heal. I would be cautious before that time least you may cause further injury. Consider using a "turf toe plate" in your sneaker.....This will decrease the ability of the forefoot to bend hereby protecting the toe.