In 2001, my then-12-year-old son and I did pretty much the itinerary you're talking about. From Portal to Trail Camp, with full packs, it took us about six hours, but that included lunch plus most of an hour hunkered down at Outpost Camp while a thunderstorm blew over.
The next day, we headed up to the summit. Leaving camp about 5:45, we were on top at 10:45.
If we were to do it again, we'd probably shave an hour off each of those times, but at 14, he's now a couple of inches taller than I am and can outwalk me on the flat or uphill below 12,000'. (Above 12k, I know how to pace myself better and take fewer breaks to catch my breath than he does.) I have a good calibration on that since we just did Mt. Elbert (14,433') a couple of weeks ago. With day packs, it took us just four hours flat to go from 10,000' to the summit on the five miles of the North Mt. Elbert trail.
Good rule of thumb is to figure 30 minutes per mile plus 30 minutes per 1,000' of gain. Add in time for meals, if any and you'll be pretty close. Portal to Trail Camp is 6 miles and 4,000', so about five hours. Trail Camp to the summit is another 4.5 miles and 2,500', so about four hours, but fudge that upward a bit because you're
starting at 12k!
Trail Camp is alpine...no trees...rocks and sand. Outpost is down in the trees but has tons of mosquitos. Personally, I don't mind the austere landscape at Trail Camp, but that's just my view...
Photos and a trip report are under the "highpointing" section of my <a href="http://www.mtritter.org">WWW page</a>.
