Well, I am a professional engineer and I stand by what I said. 28 days is to use it to lift a vehicle, but the lift can be installed on 7 day concrete. See the chart to understand that at 7 days, the concrete has about 60% of the 28 day strength. So for 4,000 psi concrete, it would have 2,400 psi strength at 7 days. Assume if you will that the lift equipment weighs 2,400 pounds and all of it would sit on the slab on just 1 square inch, the slab could carry it right on day 7 after it was poured. But the equipment will probably occupy closer to 2 to 4 square feet, so at that point, the slab at 7 days can carry 690,000 to 1.4 million pounds on that footprint. Of course if you start getting up to these weights, you have bending and tension forces to worry about beyond just compressive force, but the lifts won't weigh anywhere near this range.