It really depends on the details of your system... mash tun geometry, sparging equipment, drainage equipment (manifold, false bottom, etc). I fly sparge 10 gallon batches (about 14.5 gallons into the kettle) in about 30 min. That's about the same time as a double batch sparge (from what I hear). My efficiency is high 80s to low 90s depending on the beer.
I know that's against convention, but I know it works for me and, with my system, it makes sense that it works. I used to do 90 min. sparges and decreased my time over a series of batches until the mash tun valve was open all the way. My efficiency was virtually unaffected (maybe a point or two). I have a cylindrical mash tun, a false bottom, and my sparge is done simply with tubing from the HLT... sprinkling the water manually and randomly over the grain bed. I purposely allow the flow of water to disturb the grain bed at random various points all over the surface area of the grain bed. I believe this helps push the wort down quicker. There's another brewer on here who does it this way and has the same results.
If I used a sparge arm and/or had something other than a false bottom in the mash tun, I wouldn't expect the same results.
So, depending on your system, you could start slow (90 min. or more) and over a number of batches, decrease your time by 5 or 10 minutes until you see your efficiency affected.