Hi, My Princess Jaida is 4 months now and i am ...

Hi, My Princess Jaida is 4 months now and i am breastfeeding her - occasionally giving her formula. She weighs 5.5kgs and her birth weight was 3.335kgs. She is feeding approx 10 mins each side(sometimes less) on each breast. I am worried she is only getting the foremilk and not the hind milk as someone told me they have to be at least on one side for 10 mins to get the hind milk - does anyone know if this is true? And what is the benefit of the hind milk? How can i get her to stay longer to get the hind milk if she requires it. She is having 6 feeds per day every 4 hours and is qjuite content with this. Anyone have any ideas?