Although you can probably get away with not waiting very long, I beleive it is worth a sound mind to let it properly dry, especially if you lay it on a little thick. Just imagine you cement everything together, and eagerly start pumping water through it with no leaks and a job well done, but months down the line that cement didn't properly seal and the joint eventually starts leaking and then you have to start all over.
Read the directions, follow the directions, USE PRIMER, and don't be in too much of a hurry. I am talking from too much experience on the eagerness side in this hobby. I already had to replumb my overflow and return.