Countdown Timer that updates every certain day

I am trying to make a countdown on a text label that updates every Wednesday and Saturday.
The format is “00:00:00:00” (days, hours, minutes, seconds)
How would I achieve this?

Any help is appreciated.

Get the time using os.time()

It has a few different time formats so make sure you pick the right one, other than that you just have to get the difference in current time and the time an event is set at

Can you show me an example of what you mean?