Most garage floors are four to five inches thick which is more than enough to carry the weight of cars. If you install a lift and you know it's footprint, just create 18"x18" pads which are 12" thick under the posts. This means dig down eight more inches and also install a crosshatch of 1/2 inch rebar on 4 inch centers in these pads. This will save you a lot of money over pouring a thicker floor throughout the garage and will give you a nice foundation for your lift. Or, just pour a six inch thick floor all over. Make sure they use wire reinforcing mesh throughout the slab.
Six months is way more than you have to wait. That time span gives you a "full cure". After just a few weeks, your slab has cured enough to carry the kind of loads you are talking about. A good example is an interstate highway. They will pour a new section as part of a repair job and have cars and trucks driving on it a couple of days later.