Ultimately, I’d say a minimum of 30 minutes to a maximum of one hour, depending on the individual. As for how many days per week, a minimum of 3-4 days is the recommended amount, but it’s best if you can exercise six days a week and take one day off to rest.
It’s important to also have a well-balanced exercise routine. Optimally, you’d want to do three days of cardio exercises and three days of strength training exercises, alternating between the two. Both cardio and strength training routines have their own merits, so it’s best to not strictly stick to one or the other.