By definition a bounce takes time to detect. And you will get multiple bounces over a time period, so there is a tradeoff between latency and false positives and false negatives. As such, there must be a measurable latency in all debouncing mitigations. But depending on the switch this latency might be measured in microseconds, so you’re sort of right that debouncing doesn’t have to add significant latency for good switches and a good contoller. For a bad switch, and a slow controller, you might start to get into the ms range to ensure a switch is pulled high/low reliably.