Weylin,
The surface should be hard before you put on the next coat. In the current conditions we have in Portland, that's about 2 coats per day. In warm and dry weather I can get about 3 coats a day. If your surface is still soft after 24 hours something is wrong - either you put it on too thick or the wood is oily. With oily woods such as ipe I first seal the surface with shellac before applying Tru-Oil.