I can't honestly say I've done succession planting, I usually sow corn just once, in early June, but I highly doubt you would get a mature crop on the second planting if you waited until the first was knee-high. Knee-high in Puyallup and Kent, where I have gardened, is usually mid July or so.

It might be theoretically possible if you planted the early crop in May and kept them under a plastic cloche and then seeded a quick maturing variety no later than Mid-June. Still, given that corn needs a certain amount of "heat units" or some such term meaning "more summer than we usually get", you will likely get a good crop in late August thru September in a good year and that's it.

I'm not saying it's hard to grow corn here. It's really not, but getting two crops separated by much time would be tough.

I read somewhere that doing a single planting but including various strains that mature at 2 or 3 different times (each a couple of weeks apart) could extend the harvest period of sweet corn around here. Still would need to use corn strains that are relatively short time to maturity, and the harvest at each time would be smaller, but I liked the idea of enjoying fresh corn over a longer period. Worth a try?