Debounce time on button_a.is_pressed()

I'm using the buttons on MicroPython to measure the time of an external event (reaction based). Does anyone know where I can find the debounce time in the MicroPython code, as I need to account for this debounce time in my calculations. (Specifically debounce time on button released, if any).

i.e. something like this:

```
start_timer()
while True:
if button_a.is_released():
stop_timer()
break
```

Thanks.