normally I drink my bowl in about 45 minutes to hour, but I have done that in 30 minutes before. It made me a bit nauseas so I try to space it out a bit more. That Loa Waka is strong and can easily make you sick or nauseated if you have too much at once.
In my case I do a big amount of grog with 3-4 tablespoons through the kneading ritual and then I add 1 or 2 if the first amount (2 big "shells") is not enough. I drink it as fast as possible first and the second round more slowly, to avoid stomach fuckery. The time between rounds is usually not so much, 20-30 minutes. More is a bit pointless in my case, and less is not enough.
I love having a 4Tbsp shell at once sometimes. It is a meditative and personal journey, and usually requires one or two more shells just like it to be what I wish it to be. It settles into a nice kava groove. This technique is more aggressive than mixing 8Tbsp in four shells worth water and drinking it in a couple to a few hours.