Depending on the drying process you use, & the amount of heat used, it can take anywhere from 15-20 minutes in or over a fire, to two weeks or more hanging. When the corn is dry, it is noticeably smaller, shriveled, & much harder to the touch. If it is dried on the cob, it will come away from the cob with very little effort.
Corn hung by the gathered husk on a line in the author's home near their heater.
The same corn dried on the cob.
Dried corn removed from the cob.