The higher the temperatures, the faster the conversion to sugars. 90 minutes is PLENTY of time for full conversion, especially considering the fact that the conversion will continue to take place during the sparge (not splarge
).
60mins at 150 is plenty of time to not have to worry about conversion.
I usually sparge with water at 175-180degs to raise the grain temp as much as I can - and even then, the entire grain bed actually never reaches the 168degs needed to stop conversion.
Here's some unsolicited advice: use recipes as a guideline, but don't get too reliant on them, and learn to formulate your own. You will NEVER duplicate a given recipe by any brewer, given homebrewing conditions. NEVER. You'll get close maybe, but there's too many variables that will contribute to it tasting different. Just a few: Your mash will be at a slightly different temp, your water chemistry is different, your ingredients are a different age, your fermentation temps will be most likely different, different amount of yeast to start, different "house flavors" (from bacteria/yeast in the air), aeration will be different, blah blah blah.
Use recipes for the first few brews, but try - as soon as possible - to create your own. If you use good practices and common sense, your beer will be good. Best way, IMO, is to brew up a simple beer with just a couple ingredients and try to perfect it and experiment with it. For instance - do a Pale Ale and maybe use 9-10lbs of 2row and maybe 1/2lb of crystal malt (maybe more if the L is lower, like crytal 40, for instance), mashed at 148-152degs. Toss in some mid-high alpha acid hops at the start of the boil, and finish with 1/2-1 oz at the last 5 mins and another 1/2 - 1 oz after flame out. Simple and good. From there you can start adjusting things. For an easy stout recipe just do the same thing but use 1lb of roasted instead of crystal and no finishing hops, mashed at maybe 156-158degs.
I see sooooo many recipes that have a bunch of different grains and hops and new brewers follow them religiously, and maybe make good beer - but they don't learn about what those grains actually are doing. Usually all the different grains and hops just get muddled together and you can't really tell what they are contributing.
Keep things simple and stay away from the complicated stuff. Learn simple beers first, and you'll find that those simple beers are generally better and more satisfying than the complicated ones. You'll learn alot more, too.
Once you've brewed several batches and you think you're going to stick with it, invest in a refrigerator with a temperature controller to ferment in - and maybe turn into a kegerator. Besides obviously sanitation, there is nothing that makes more of a difference than fermentation temperature control!
