Car either hesitate to starts or won't start after being driven for a bit then turned off for 15 to 20.

From the details that you are stating, I am believing you are having an electrical issue. Not your spark plugs but your plug wires or coil. I would venture to check them. Look at all of them carefully to see if there is hidden fraying, push the terminals out of their rubber boots to examine the tips. I don't want you to spend money on wires if you don't need them, but that is what I would suspect is an issue.

I have much the same issue with my 2001 Tiburon. After about 5-6 hits on the starter, it will sometimes start when hot. Sometimes it will run after choking for a few seconds, then catches runs fine? Otherwise, have to wait an hour or two. I suspect either an air or fuel problem but just don't know where to start.