It took about 30mins to install my efan. That included wires and all. AS for putting the stock one back on... it just threads back on the pully, and 2 bolts with abut 5-6 plastic push pins. It shouldnt take more than like 10-15 mins to revert back and forth, since the hard stuff is allready done.
After I get cam installed I will make an appointment with Allen at Nelson performance to get a dyno tune. Im sure he would not mind too much.