Hello JenLovesSummer

30 minutes a day is recommended for woman to maintain a healthy heart. (remember this is a loaded statement and can drastically change depending on the individual.) But, 45 minutes to an hour are recommended if the same woman wants to lose weight. When the studies say 45 minutes to an hour, they mean at one time. Because it takes some time for you to get your heart rate and breathing up to the proper level and your muscles loosened up, it is typically better to exercise in one longer shot than many small ones. (again this is another loaded statement and can change drastically with the individual.)

I hope you found this helpful