Interesting question. I put polysorbate 80 (Inner brand) on when I first get up in the morning and let it soak for about 20-30 minutes before rising it out in the shower. (I have my coffee, shave etc....then shower.) It is great for my scalp and hair. The longer I leave it in, the greater the benefits. I do not know if there is a margin of deminishing returns.
I remeber reading that Polysorbate 80 was first used widely as a preservative additive in foods. I would not seem to hurt leaving it on all day.