I have noticed the wait to start light stays on longer and when I hit the key it doesn't always start. I can hold the key in the on position for up to 10 seconds sometimes before it will start. Is this an ignition switch issue? Most of the time it is cold starts when it happens.

Make sure your intake heater is working...although a Cummins should start easily without the heaters even if it's below freezing a few degrees .
I'd be suspicious of a fuel drain back problem or a lift pump issue.
Have a qualified Cummins mechanic have a look at it.

I'll plug it in and see what it does

No...not the block heater...the plenum heaters in the intake....Cummins version of glow plugs.
I guess you could try plugging the block heater in and see if it helps. But as I said, a Cummins should start pretty easy at 32*F WITHOUT the heaters coming on. If it doesn't, you have a fuel supply related problem. I'd get the pressure at the lift pump checked at the very least.
My '92 got hard to start a while back, and we traced it to a bad o-ring seal above the fuel filter/fuel heater plate. Air would get into the line overnight and it would take some cranking to get the old girl to start. Once air gets in there, the fuel will siphon back in the line. Check all your fuel banjo fittings....one could be loose.