What is the proper procedure for steeping specialty grains while extract brewing?
Temp, time, grain bags or not.
I don't know if there's a "proper" way to do it, but I've always used a grain bag with good results up until my most recent batch. Time and temperature vary based on the grains being used and desired flavor profile, among other variables.
For my most recent batch I steeped 2 pounds of specialty grains in 3 quarts of water in a separate pot, drained this through a cheesecloth-lined colander into my brew pot, then rinsed with 1.5 quarts of 170 degree F water. I don't know if it made a difference, but I kind of liked doing it this way. It seemed like more grain surface could come in contact with the steeping water to allow for more flavor extraction. It's kind of like how it's better to steep tea in a filter cup than in one of those tea balls.
So, from a different perspective, steeping grains is just the same thing as mashing, you're just using a bag to remove the grains rather than draining the water from the grain bed.
I'm also not sure that there is a "proper" way, but just like a mash the temperature and amount of water you have mixed in with your grain makes a significant difference in what you get out of it.
During a mash you're converting starches in the malt to sugars and there is a specific temperature range that works very well for that. In your grain bag, you're using entirely specialty malts, so there will be very little starch-sugar conversion going on, because those malts do not have the diastatic power to convert their own starches, so you don't necessarily need to worry about it as much, but if you're temperature is too high, you're going to leech a lot of tannins out of the grain in addition to the flavor compounds that you're looking for. 170F is probably about as hot as I would get it. I'd shoot for 150F - 160F.
You also want to make sure that your grain isn't bound too tightly inside the sack. You want to make sure that the grain has as much surface area as possible in contact with the water. Leave it in there for an hour, and you're probably fine.
Back when I was doing partial extract, before going to all-grain, I was putting a small amount of normal pale 2-row malt into my grain sack. Pale malt has lots of diastatic power and can help starch conversion with specialty grains. You still won't get enough out of it to not also want to use malt extract, but I always found that I had a much fuller flavor from my specialty grains when I supplemented them with 10% -20% extra pale malt.