We all get super busy sometimes and weeks may go by without us getting a workout in. Often this is one of the prime reasons a person hires a personal trainer...simple accountability...knowing that someone is there at the gym waiting for them with an appointment.
Truly, if you only have 5 minutes and can simply do 25 bodyweight squats, 25 crunches, and a few pushups at least your body is getting its metabolism spiked and you are stimulating positive fat burning and muscle building hormones.
At the end of the day, there is not such thing as "not enough time". You can literally get a workout done in 2 or 3 minutes. Obviously its even better to spend 30 minutes in the gym, but still, 3 minutes in your living room can still get your metabolism going.