The correct term to use for concrete "drying" is curing. Concrete cures as it hardens and doesn't dry.
After the concrete is poured in place, at 70° F, it typically takes about 8 hours for the concrete to cure enough to support foot traffic and not leave some type of footprint in the concrete.
Once the concrete is allowed to "dry" for 24 hours it will support normal foot traffic.
After 48 hours of cure time you can start to build on it or begin to set heavier loads on the concrete.
Between 3 - 7 days of cure time you can drive on the concrete with smaller vehicles to larger trucks.
At 7 days of cure time most concrete has reached about 70% of its full strength and sometimes even more.
At 28 days of cure time (or drying time) the concrete has reached full strength and is considered fully cured.
I pour and finish a lot of 4" thick concrete floors, slabs, and patios. The time it takes for 4" of concrete to dry (or cure) is really dependent on the temperature.
This garage floor took us about 30 minutes to pour and level. Then it took about 1 to 1.5 hours before we started finishing & troweling.
The troweling process took about 2 - 3 hours from start to finish. We started pouring at 7am and finished power troweling about 12pm. It was 70° F when we started and 80° F at noon.
At normal temperatures (70 degrees F°) a garage floor like this will be hard enough to walk on in 8 hours. By "walk on" I mean you won't leave a footprint but it will be easily scratched or damaged. It's still what we call "really green".
Most normal foot traffic can be done after 24 hours of cure time although 48 hours would be better.
In colder temperatures below 60 degrees F°, I would double the times above for use.
It takes between 24 - 48 hours for a broom finished concrete driveway, patio, or pool deck to cure before you want to walk on it.
I would recommend waiting a full 48 hours before attempting to walk on new concrete that's got a broom finish, 72 hours would be even safer.
The reason is the surface of broom finished concrete is less dense than hard troweled concrete. In other words, it's "softer" and more likely to be damaged from foot traffic.
Giving the concrete 2 - 3 days to cure ensures the surface is hard enough to take foot traffic and not get scratched or gouged from shoes & boots walking on it.
I'd wait 7 days to drive on a new broom finished concrete driveway. The vehicle weight combined with turning tires could leave behind some damaged areas if you try driving on it sooner.
Concrete should cure a minimum of 24 hours before you put any weight on it. I'd keep the weight under 100 lbs. at this time frame.
Be careful though, the concrete has only reached a small fraction of it's strength at 24 hours and could crack or break if too much weight is put on it.
You're better off waiting 48 to 72 hours if you really need to put any type of weight on your new concrete. After 3 days of curing most concrete pours can withstand putting a small car on it. (it's better to wait 7 days for cars and trucks if you can)
@ 7 days a 3000 psi. concrete mix should reach about 2500 psi. strength
@ 28 days a 3000 psi. concrete mix should reach 3000 psi. strength (or full strength)
Walk on time will depend on what type of concrete mix you use and the outside temperatures. But in general, here's the walk on times for some different types of concrete mix designs.
All these concrete "walk on" times are based on using them in temperatures at 70° F.
If you're asking the question Can I walk on concrete after 12 hours, the chart above will tell you which concrete mix you need to use in order to be able to do that.
If you need to "speed up" the set time of your concrete there's a few things you can do to make concrete dry faster.
The length of time it takes for concrete to dry after it gets rained on will depend on when it rains on it and how long it rains.
If it's during the pouring process then this will increase the mixing water as the rain mixes with the fresh concrete. If it's a short shower then the dry time may only take and extra hour or two than normal. If it rains for and hour or more then the dry time could take 2 - 6 hours longer depending on the length of the rain storm.
If it rains after you get the concrete poured but the concrete is still very soft:
If it rains after the concrete has just been broom finished you will need to cover it with some plastic to protect it. Then you may need to touch up the broom finish afterwards if the plastic causes some unsightly marks.
If it rains 2 to 4 hours or more after a broom finish the concrete should be hard enough to withstand the rain with no damage at 70° F.
If it rains after you complete a very smooth power trowel finish, the concrete should be hard enough at this point to not get damaged.
The length of time it takes for concrete to dry after it rains is different in every case. It depends on when it rains in the process, how long it rains, how hard it rains, is the concrete covered or uncovered, does the rain damage the surface, there's so many factors to consider.
It's best to never pour any type of concrete in the rain. Another tip is to never take a chance if rain is in the forecast. Concrete can get damaged and ruined if it gets rained on.
The drying time for a concrete fence post mix varies depending on type of concrete mix you use.
The "no mix required" bags of concrete means you dig your hole, insert the fence post and brace it off, add the dry concrete mix around the post and pour some water on top. Backfill and your done.
Refer to the manufactures data sheet for specific and more detailed instructions for use.