The Jack Keller Extended Instructions is one of many approaches for extending kit wine making time. For example, WineMaker Magazine has a 90 day schedule. I believe most kit wine makers with more than one or two kits always follow an extended schedule of one form or another. Keep in mind that kit wine makers want to sell kits and offer an approach to get kits finished quickly, but not necessarily at their best.
Depending on the kit it may not only make a big difference, it's just about required. Choose an approach and give it a try.