Are you in the Twin Cities? We have lots of clay here. Clay never really dries out ;)
Looking at the concrete, notice how it's flared at the top, this is a nice 'handle' for the frost to grab on to and push up. Ideally, your flare would be the complete opposite...wide at the base of the hole, narrow at the top.
If it's really heavy clay, you may want to forgo concrete completely and instead use compacted crushed rock.
If you stick with concrete, be sure to dig deeper than you need to and put gravel at the bottom of the hole for drainage before putting in the post and concerete. Also be sure to get at least a good 2' of the post into the ground.
Several things affect the final weight of concrete.
Concrete has many different densities based on its composition. Standard "ready mix" concrete is often engineered for structural strength of 3000psi. Since concrete is not this strong when it is first poured, a standard was created for when to test concrete. This standard calls for the strength to be determined at 28 days old. At this point, concrete has achieved about 99% of its strength, and will continue to very slowly strengthen over the next few years. At 28 days old, I use a density of .085 pounds per cubic inch (146.9 pounds per cubic foot) when calculating structural load.
Concrete is porous. In humid weather, concrete will absorb moisture from the air while in dry weather it will release moisture. Even if you made the "perfect" weight today, it may decrease or increase over time. This is why, when you buy concrete weights, they are encased in plastic.
Regarding your question on adding more or less water: Contrary to popular belief, concrete doesn't "dry" to for it to cure. Concrete hardens as a chemical reaction. Adding more water than what is optimal to create the chemical reaction will only weaken the concrete without changing its final weight.
As a side note, concrete cracks easily. This is another reason why, when you buy concrete weights, they are encased in plastic. With that not being a reasonable option here, and based on your application, I would strengthen the concrete mesh or fiber. You can order "ready mix" with fiberglass fibers in it, or you can use a large hole mesh. Too small of holes will create a fault line. Aluminum works well because its density (.097) is close to concrete's density. In any case, this type of weight is not to be dropped from any height.
Best Answer
The odor is a function of the drying process. Some moisture is chemically bound to the cement, but some remains. The dryer and breezier the area is the quicker it'll disperse. We can't really say.
It is odd that the cement is so smelly that you notice it. A new basement slab smells like fresh concrete for weeks or years, but that small patch shouldn't really be noticeable if there's any ventilation at all.
You could coat it with a sealing primer, then paint it to help block the odor.