The ACI sells it for $58.50. There are other construction book sources but I doubt they are cheaper. It's not a long document so if you have specific questions I may be able to answer them or post a section from the standard or other ACI standards. Hopefully your contractor owns a copy. In many areas the soil at footing depth is consistently granular, well drained, and free of organic material. It can usually be verified by sight, smell and feel (if it's black, squishes through your fingers, or stinks, you have a problem). Sometimes there can be a layer of organic material from the bottom of a swamp, etc. and it must be removed. Organic material will continue to decompose and will allow the footing to settle. Reinforcement in the bottom of a deeper footing can help bridge local areas of poor soil but not larger ones. Deeper in the ground is also better and so is reinforcing in the stem wall but if you build over an underground stream or a sink hole all bets are off. Relax, I'm joking. A geotechnical engineer is only needed when the person in charge of the design or construction is in doubt. I've only hired one when the soil didn't look like we expected it to. I've only drilled for soil analysis samples for a multistory commercial building. Here is a link that might be useful: ACI 332

I would let it "sit" for at least a week, but wait as long as you can. It's hard to really say how long it will take to fully cure, but based on your description, I would say that you have done a great job. Technically it can take a full month to cure, but use your judgement, the surface should (obviously) not be tacky. If the surface is flat and you want extra protection, I sometimes use a piece of glass, which I know can be expensive. But I also like the "antiqued" look.

dianlo is somewhat mistaken. While latex drys faster than oil it actually cures slower. I would wait a minimum of 10 days with oil and 30 days with latex for heavy items like cans, plants etc. I f you plan it out m, you can always paint an extra scrap board and see how long it takes for that to be hard and not mark up. Personally I prefer oil paint on good shelving. Especially if you live in a humid area. BM satin Impervo looks and lasts better than any water based paint. ( I'm a retired painter) A good suggestion for shelves is a water based porch and floor paint if you don't like oil. I painted a 2 car garage that had bare plywood shelves built on all 3 sides floor to ceiling with am porch and floor acrylic latex.( It's a garage after all) 2 coats primer, sand between and one finish and it's still looks great 8 years later

@User Thank you for your response! I don't know the method yet, but I was surprised when talking to one contractor and he said the next day you can put a bathtub on the new concrete that was poured in the roman shower. I just wanted to ask on Houzz to get a ball park so I know to hire someone that knows what they are talking about. StarCraft Custom Builders above wrote 3-7 days. Do you think that sounds about right depending on the method, etc, or could it be longer? It's great to get a second opinion. I really appreciate it. Thank you in advance for your response.