The New York Times reported on two new studies found that it may be just as effective to do both on the same day. There has been a common thought that you need to separate strength training and cardio days in order to achieve the most benefit (known as “muscle interference” or “exercise antagonism"). It has also been thought that combining strength training and cardio may have a negative effect. These new studies show that there are similar gains combining cardio and strength training while putting in less time than when done separately. People who did cardio and strength training on the same day did half the amount of each compared to the other subjects but still had the same overall benefit.
So when deciding how to exercise when you have limited time, do your cardio and strength training on the same day knowing that you're getting the same benefit for half the time commitment.