I think that waiting the full hour to hour and a half as people suggested is potentially a bit overkill. For some people this may be the case, but by half an hour in nowadays I feel completely back to baseline. I guess if you're one of those people who take longer to work it out of their systems, you should wait all the time you feel necessary, but personally half an hour and I'm at baseline. It may not be the same baseline I had before trying spice, but my entire day, whether or not I touch spice or mj or alcohol (or whatever) for over a week is still populated by mild phosphene clouds of color.
"Science without religion is lame. Religion without science is blind" - Albert Einstein
"The Mighty One appears, the horizon shines. Atum appears on the smell of his censing, the Sunshine- god has risen in the sky, the Mansion of the pyramidion is in joy and all its inmates are assembled, a voice calls out within the shrine, shouting reverberates around the Netherworld." - Egyptian Book of the Dead
"Man fears time, but time fears the Pyramids" - 9th century Arab proverb