Fitness

You don't have to go to failure for gains.

You don't. This article is about saving time, not things you have to do to make gains. You can compensate for doing fewer sets and lower frequency by going closer to failure. It may not be ideal, but neither is only having an hour per week to workout. You do what you can given what you have.

missing warmup

Huh? The article says "put all Wolf's advice together, along with a good warmup".

How do you squat and others only with dumbbells?

Either have untrained legs, or don't do it with DBs. If you need to do barbell squats, you just have to accept that it'll take longer.