You've gotten good advice so far.
Dunno about sealer, but for the summer heat, keep it damp for the first few weeks for it to cure evenly. Just mist it with a garden hose often.
Never heard of waiting 30 days around here the last step before the floor guys leave is to seal it.
In basic terms, concrete gets stronger the longer it is kept wet. When they talk about a 3000 psi mix, they mean the concrete will reach or exceed that strength if kept moist for 28 days. As Charley pointed out, keeping it moist also helps prevent surface cracks from forming.
Around here, virtually all professionally-placed concrete is sprayed with a curing compound as soon as it's finished. The curing compound is essentially a sealer that helps hold the moisture in the concrete for the initial cure...generally a few days to a week. It doesn't looks like the concrete is sealed, but it does the job. Covering with sheet plastic and occasionally moistening the surface (as Charley described) is also effective, although a lot of commercial outfits prefer the curing compound, since they're no need for follow-up visits to the jobsite. A bit of concrete science: Concrete never really dries, it cures. With the exception of a little bit of surface moisture, the water in the mix doesn't evaporate. Instead, the water causes the hardening of concrete through a process called hydration. Hydration is a chemical reaction in which the major compounds in the cement powder form chemical bonds with water molecules and become hydrates or hydration products.
Thanks all for the advice. The pour went well today. They made quite a mess in my yard but other than that I'm hoping for good results. They will return tomorrow to remove the forms. We have rain expected over the next couple days so I'll have to ask them if it needs to be covered.
No need to cover it to keep the rain off after about the first 24 hours. The rain will be good for it, and occasional moderate misting with a garden hose (if it's not raining) doesn't hurt either.
How well the surface holds up over the years is largely controlled by how wet the mix was to begin with (as Charley described) and also on the techniques used to finish it. If the guys who placed it are pros, I suspect they knew how to do it right.
On the subject of soupy, or watery-looking mix coming off the truck, Charley is right about the more water the weaker the finished product. There are some exceptions to this, though. If they use additional cement powder in the mix, that can make up for the extra water. Another way to have soupy, yet strong concrete is to use chemical additives called plasticisers. I've worked on commercial projects that used plasticisers resulting in a mix so soupy it looked like fresh cow poop, but once cured, it was very strong. That said, the chances of your contractor using extra cement or plasticisers is pretty slim, since both of those add to the cost per cubic yard.
Personally, for an outside slab, I wouldn't bother with any sealer beyond the initial curing compound.
On the subject of control joints (the saw cuts or tooled joints Charley mentioned), a good rule of thumb is to have the joints spaced at 24 to 36 times the thickness of the slab. So a 1" slab would have joints every 2 to 3 feet. A 4" slab would typically have joints every 8 to 12 feet. (So the 10' number Charley gave would be right on the money.) Another thing to keep in mind is that by their nature, concrete slabs want to be square. Because of this, it's best to try to place the control joints so as to create square shapes (or something close to a square). For example, on a 3' wide sidewalk, ideally the control joints would be every 3 to 4 feet, even though the "rule of thumb" says you can go up to 12 feet between joints (assuming a 4" slab). But on a 24' x 12' patio slab, you could probably get away with a single control joint, splitting the slab into two 12' squares. (Personally, I'd probably make it into eight 6' squares instead of two 12' squares, though.)
I hope this helps.