I know it seems impossible, but this afternoon I built two wheels from scratch and had them on my bike in 3 hours, that's 90 minutes per wheel. This isn't the first time I've done it this fast either. Here are some helpful tips to make things go faster.
First, make sure you grease all of your spokes. Next, lay the hub down with the rim around it and put the "inside" spokes in (the spokes that are cleser to the middle of the hub) the side that is up. Find the holes in the rim that are pointing up and towards the spoke. They should match up with the spokes you have in the rim so far. Put nipples on the spokes, but only spin them on a little bit, just enough to keep them from falling off.
Now flip the wheel over and put in the inside spokes on the other side. Again the holes in the rim should point directly to the spoke. Put nipples loosely on these spokes as well.
Now put the outside spokes in the side facing up and put the nipples on loosely.
Now flip it over and put in the last set of outside spokes and put the nipples on.
Now for a very helpful hint that will save you tons of time when truing. Tighten all of the nipples until you can see 2 threads sticking out above the top of the nipple. Spokes are pretty close to the same length, and with them all tightened the same amount (but still pretty loose), you will have a very good place to start from when you go to true.
Now it is time to true your wheel. You don't need a fancy truing stand for doing one wheel, a pencil and your bike will work fine. Put the wheel on your bike and tape a pencil the the fork or swingarm so that it acts as a pointer.
Spin the wheel and watch how much it moves up and down. Tighten the spokes at the high spot and loosen the spokes on the other side until it doesn't move up and down anymore. It should be very close if you tightened all the spokes evenly as mentioned before. Next, look at how much the wheel wobbles. This may be pretty far off, but is easy to fix. tighen the spokes on the side that you want to pull the rim to. Once you get the hang of it it's pretty easy and won't take long. It normally takes me 10-20 minutes to get it straight. Once it doesn't wobble, double check that the wheel still doesn't move up and down. Next, start from some point (like the valve stem hole) and tighten every third spoke a little at time. Go around the wheel three times (when you get back to the starting point you will have to go to the fourth spoke so you don't keep doing the same spokes over and over). If a spoke feels really tight already then skip over it, if it feels really loose, tighten it a little more than the rest (a spoke torque wrench works well here). You may have to do this part more than once to get them all tight. By doing every third spoke you keep the wheel true. Once it is tight, double check again that the hweel is still true.
Now you are set to pull the wheel off the bike and put the brake disc, sprocket, rimlock, rim strip, etc back on. Mount up the tire (careful not to scratch your new rim of course).
Now all you have to do is throw it on the bike and you are set to go.