With (land!) crab tanks you don't need to establish bacterial colonies in a filteration system to cycle ammonia through the Nitrogen Cycle (TM); the crabs aren't in water where ammonia waste is aqueously supended, so their own excreations wont build up and kill them.
As soon as the air temp is in the ballpark & humidity is up, they can go in.
But you should of course clean up their poop. And use a dechlorinator that mitigates ammonia in tap water... because their bathing water is ingested and used to moisten their gills.
Preferably the tank is stable (temp and humidity not fluctuating much) before the crabs go in. If you can give it a day or two that's great - but if the crabs gotta move, then the crabs gotta move.
As for how long stabilization takes, it depends on the tank & ambient conditions. You may find yourself fiddling with heat & humidity for a while after setup (like if your ambient humidity is super-low, or if your room temperatures vary considerably from one day to the next, making consistent heating an issue). But as mentioned, larger tanks are much easier regarding stability.
Ok, so my friend got 5 hermit crabs from a pet store. I went to her house and she had ALL of them in a critter keeper. I told her she needed a bigger tank. Long story short, I traded her a 29 gal tank for 2 of her poor crabs. I am a new crabber, but research everything before I commit. So my 2 crabs got here and one immediately went under, normal behavior. The other one went under that night but, I see him from time to time. The one I took from her because it was so stressed, is the one the buried himself, I honestly believe he buried himself to die. Lol. I know he could be molting. But I don't have high hopes beings he has been under going on six weeks. So fast forward to today. I went to her house to give her some sardines that I opened and don't want in my fridge an she tells me she only has one crab left and to take him and the stuff. So now, in my 10g tank I got the small one I barely seen, the one possible molter, and the biggest hermit crab I have ever seen!!!!! Obviously I need to move them to the 29g but I am waiting on myheater to get her because she had nothing..... So finally to my questions. My 10g tank conditions are perfect 82/84 sub is 6 inches which was actually about 4.5 times my crab. Now I have this big guy so I know it isn't deep enough but I'm setting up the other tank tomorrow. What I need to know is how long after I set the tank up can I move them? Do I wait a couple days, a week, do it right away??? And I also need to know if the 24 watt heater on the outside is gonna keep my tank warm. I never had problems with the small tank so I'm worried the bigger tank maybe an issue. The new crab is doing great, he is constantly switching between shells and I have noticed that my little guy have been up all day with him so I'm glad he has a friend. My next question is the one that's been down. When I change tanks I wanna empty the 10g till we move. I obviously know we shouldn't dig, but the tank needs to be moved reguardlees, so, any suggestions on that in case I dig and he is actually alive...... please help. U am honestly just trying to give them the best life they could have in captivity 
This morning I woke up to find the cuttle bone half way across the tank. I see a lot more cleaning up the tank with him around 
Can't wait to get off and open my boxes. The set up a new tank. My favorite. Lol
Humidity is high 80s , we looking good so far!!! Oh yeah, unfortunately the buried crab was a goner. But I took him because he was so scared so it was no surprise. Now my son want me to set him up the pc in his room. He says it's not fair I get a pet and he doesn't 
After the move huney, little does he know, I got me a 65 waiting for after the move. Lol. Now THAT is gonna be fun to decorate. Lol. Thank u all so much for your help. This site is AMAZING 
