Here‘s how wait time works:
Unity has its own internal clock, which can be manipulated to do e.g. slo-motion effects, pausing the game etc. This clock is called time scale, and you normally use this. But some stuff still needs to wait, but should not be affected by Unity’s internal time, which is “real-time”.
Say a puzzle must be solved in 30 seconds, but the game is paused. Of course, the 30s timer should be paused, too. But the UI has 2 second delay for some effect, and this should always be 2 seconds, in “real-time” no matter what.