Back in the old days, people used low-cost switches unless they could not avoid it. With keypads and keyboards, it was pretty important to have switches with very similar characteristics for the very reason that firmware scanning and, in fact, scanning in general, made this pretty critical because it was necessary in order to discriminate between overlapping bounces versus overlapping (multiple) keypresses, which had to be handled differently. Back then, when air was clean and sex was dirty, 20 ms was considered a reasonable debounce interval. If you can't get the manufacturer of your switches to provide reasonable estimates of contact bounce timing, you might want to look at one or two of them under "normal" operation, with a storage 'scope just to see how long it takes the contacts to settle.

If it's a long time, perhaps the RC circuit is warranted. How you apply it will have significant impact, too.

It's worth noting that many keyboard scanners don't encode the keypress until it goes away.

RE