How long does it take gingivitis resolve?

Don't give up! If your good habits at home, i.e. Brushing and flossing, don't reduce the problem, you may have more serious periodontitis rather than just gingivitis. See your dentist soon.
Fairly Quick. Gingivitis is a more minor inflammation of the gums as opposed to periodontal disease. A good professional cleaning and good home care will normally resolve it in a week to 10 days.
Gingivitis healing. It depends on the extent and duration of the problem. Typically, if it is just gingivitis it should improve over a few days to a week, if you are managing the problem (good home care). If you have been asked to do specific care at home, please do so. As always, it is best to haver your dentist check this regularly to be sure it is being taken care of well.