It doesn't work like that where 1/10th the dose will last 1/10th the amount of time. It will basicall last for the same amount of time as a full dose, but you won't notice the very tail end of it because the dose is so low that at some point it will be completely imperceptible.
Duration of psychedelic effects functions in something like the way the sound diminishes when you strike a bell. If you hit a bell softly, it will diminish at the same rate as if you hit it hard, but you have to put your ear closer to it to hear the sound of the softer strike. Dosing smaller amounts of drugs is somewhat analogous to that.