25 minutes - 1 hour
My sisters keyboard did not work, namely the keys she most ommonly used so they had been using the on screen keyboard. I thought that was silly so I replaced it as a christmas gift.
The repair went well except after I got the computer most of the way back together i noticed the speaker cable was pinched in the battery bay and had to take it all back apart, reposition the cable and reassemble. Total time about 20 minutes.
Just make sure the wires are all in position before reassembly :)