I have no patience when it comes to sparging 10-gallon batches. After running off wort from the lauter, I usually add back an equal volume of water to the mash and let it sit. I heat the water to 150-160 degrees before adding to the grain bed so I reduce the risk of importing any tannin. The longer I let it sit, the darker the runnings into the kettle. (Ah ha!) I've been told that, prior to the boil, there's really no harm in letting the first runnings sit in the kettle. Nevertheless, I fire up the kettle and wait for the first runnings to nearly come to a boil before adding the sparge to achieve my target kettle volume. I suspect that letting the sparge sit a while contributes to a higher OG, though I've never taken the measurements .. yet.