This depends entirely on the store and it's current condition, and how quickly you can implement things.
I end The Backdoor Method by outlining 3 implementation roadmaps - a set of short term easy fixes, Mid-term alterations and long-term strategy changes to apply to your stores.
I'd expect you to start getting more traction about 7 days after implementing the short-term plan. I'm talking a noticeable increase in visitor numbers and possibly the start of some sales momentum.
I'd then expect you to see some more substantial improvements a few weeks after the mid-term plan. The changes you make here should definitely start giving you a good level of consistent daily sales.
The long term plan is where you'll see the bulk of your progress, because this is where we focus on scaling. Substantial traffic increases and exponential month-on-month revenue growth.