Experimenting is part of the fun when it comes to fitness and exercise. You learn what works and you find out where you are when it comes to being in shape. Isometrics are a hell of a way to get in shape and will test your strength and durability if you do them right. Isometrics can also be a test of your cardio cause if you hold for a certain amount of time like 30 seconds to a minute or longer, you may find yourself breathing hard quick.
Most workouts shouldn't take too long, you do what you need to do and move on. You can also do micro workouts or shorter workouts throughout the day like doing a few push-ups and squats in between commercials, do holds, punches, kicks, burpees or do a sequence for a few minutes like a Flow using Animal Exercises and so on. Sometimes I like to do a 5-10 min workout of supersetting a mid push-up hold on my fists and a horse stance back to back doing a 20 seconds on, 10 seconds off going back and forth until those 5-10 min are done, it's a hell of a workout.
This morning after some meditation, I wanted to try something different for an isometric workout. I wanted to see how I would do with supersetting 1 min. Iso Push-ups On Fists (5 sec plank, 5 sec mid hold repeated for 1 min) and a 1 min Horse Stance for a few rounds. Managed 3 and it was pretty tough, struggled a bit on the Iso Push-ups on the last round but made it through. Short Workouts can be intense as hell even though you're not doing a whole lot but a whole lot is going on. With this workout, you're hitting major muscle groups and as a superset, you're working on your conditioning as well. Try even 1 round and see how it feels, many aren't able to do it.
6 minutes doesn't seem very long and it really isn't but when it comes to Isometrics, it'll feel like hell on earth and you're having issues holding positions that really tackle the tendons and ligaments while strengthening the muscles throughout the body. They toughen you up and give you some awesome speed and power that you don't get with other exercises. Overall, in the words of Elmo from Vision Quest "It's not just 6 minutes, it's what happens in those 6 minutes."
Be amazingly awesome and test yourself out on different workouts to learn what YOU are capable of.