90 minutes is fine, as long as you can actually stick to 90 minute workouts. For many people, this is too much to fit into their busy schedule. Your workout should only be as long as you can realistically handle on a weekly basis.
An ideal week includes 3–4 days of strength training lasting ~30-minutes each. In addition, you should try to squeeze 1-2 aerobic sessions into your routine as well.
Now let's go over how to design your workout to ensure that you are focusing only on the stuff that matters while cutting out the fluff.