This article has a lot of useful information, including how long altitude acclimatization lasts:

http://www.bodyresults.com/e2deacc.asp

Medical research (and my personal experience) indicates that a few days spent at high altitude provides little, if any, acclimatization benefit. One needs to live at altitude for a considerable length of time (weeks, months, years) to gain any significant accclimatization. Sleeping at Whitney Portal for a few nights doesn't really help the process, except perhaps psychologically. WBTravis' advice is helpful, in that several hikes to altitude will give you some idea on how your body is going to react to altitude on Whitney, and then allow you to adjust accordingly.

Don't fool yourself into thinking that a couple of days on San Gorgonio is going to help your acclimatization before you head up Whitney. It might help with your overall physical conditioning, but will not help you acclimate to altitude. As WBTravis indicated, hiking to high altitude several times will, however, give you experience regarding how your body is going to react to high altitude; then, you might have a better idea of how you are going to perform on Whitney and make the necessary adjustments.

I live at 4,200 feet, which helps with acclimatization until I reach about 10,000 feet plus. I worked for ten years at 8,100 feet, but returned home each weekday night to sleep at 4,200. The work altitude time was pretty much negated by sleeping at the lower altitude. People who live in high altitude towns like Mammoth Lakes, California, (8,000 feet Plus) have an advantage over the rest of us.

Notice from the article that acclimatization disappears quite rapidly upon descent to sea level.

My advice, for what it's worth is, if you have to travel from low altitude and then dash up Whitney, follow the basic rules (good physical conditioning, slow pace, ha ha, hydration, high carbo diet,...) of acclimatization, and descend if you start feeling ill.