If you are Fly sparging (aka: Continues sparging) you are going to be getting the best efficiency out of any other method. Now i can't give you exact numbers on your efficiency doing it this way as your system is completely different than mine, and i have nothing to base your previous method upon.
Time is also something that changes with every brewer, my guess for average sparging time is around 20-40 minutes between brewers doing 5-10 gallon batches.
I wouldn't worry much about hitting an exact time, what you need to concern yourself with is:
While you are sparging you are not creating a channel through your grain (like a under grain river of sorts) an easy way to make sure this happens is to keep 1 inch of water above your grain. Adjust sparge water coming in at the same flow rate of your wort going out.
Some brewers like to cut thin paths in the top of there grain to help make sure the water filters through more evenly.
I would recommend raising your mash to 168-170 (its advised that 170+ temps will pull harsh tannins out into your wort) and your sparge water should be the same temperature and water.
adjust the PH of your sparge water also to reduce the leaking of tannins, i use phosphoric acid.
monitor the PH of your run off wort also, this will tell you when you have rinsed your grain thoroughly enough and extracted all you need (hopefully u hit your target volume) I can not think of the PH number that is the stopping point, hopefully another member can answer that.
I hope this info helps you on your all-grain process.