I'd say that you should do it whenever you can get around to it - no real hurry but it will keep you from getting stuck somewhere and/or potential damage from overheating when the pump does fail.
I used the Pelican DIY instructions and its technically pretty easy, it just takes a several hours to get it all done. If you take your time, you really should be able to do this.
http://986forum.com/forums/general-discussions/43198-new-waterpump-t-stat-today.html