The KE lounge is basically at the walkway from TBIT to T4 (assuming your OMA flight departs from there versus T5). It's a relatively short walk. It all depends on how early you want to or need to be at the gate. I usually give myself about 5 minutes to T4, but I walk really fast. T5 will take a bit longer because you have to go halfway through T4 to the escalator, go down, and then take the tunnel all the way to T5.
It sounds like you have a fairly long layover. I'd suggest you might us PF Chang's first for some food before the KE lounge if your Priority Pass is unlimited. The food in the KE lounge is limited and PF Chang's is actually a large, open space where's pretty quiet and relaxing, especially at that time of day.