you don't have to wait at all....technically you can plant right on top of fresh food scraps....by the time the roots reach down that deep the scraps will have decomposed.

what GTD says. Roots are fine with currently composting materials, except perhaps with salty manure.

How long to wait depends on how active a Soil Food Web is in that soil. Buried "kitchen scraps" can excite the SFW and cause them to get to work digesting that material which could cause some Nitrogen to be not available to the plants since the SFW is utilizing it. A soil with not much organic matter, and a not very active SFW, will be more apt to show N deficiency then a soil with adequate levels of organic matter would when undigested organic matter, "kitchen scraps", are put in the soil.

My childhood neighbor buried kitchen scraps all summer long between the rows of her vegetable garden. The next year she moved the rows over the buried scraps and repeated the process.

So they are probably gone by now.

It's OK to keep burying them ... unless you start interfering with the roots of the perennials and shrubs by the constant digging, which won't happen for a year or two.

I think you may be surprised at how fast that stuff disappears. It happens here in the middle of growing season in a matter of weeks, even with intact fruits with tough skins like oranges and zukes. The mix of critters in the ground is a powerful one indeed.

I agree: you don't have to wait to plant. Even if you put the scraps into a sterile soil devoid of organisms initially, there will be bacteria and fungi which will quickly attack the scraps. Go for it; the soil and plants will thank you.
Renais