How long does it usually take for an xbox to get shipped back when I sent it for repairing?

Depends on where you are.It can take around 7 days up to 3 or 4 weeks.Could be longer at the moment due to the situation the world is in.

As far as i know the repair centres work Monday-Friday.

I just did a regular order repair on Friday due to power issues. My question is how long does the shipping label take to get to my house?

You can start a repair request here:
support.xbox.com/.../repair-process

Usually, it can cost quite a bit to get it repaired, since it has to be collected, sent to a repair centre, fixed, and then sent back to you. The good thing is that it is quite fast, and shouldn't take too long to get repaired and returned.

@Dr Dreso: Sorry to hear that. Does it at least say "product shipped to customer"? Apparently, the normal wait is 6 days after that update, but it does take longer in some cases. Either way, it takes too long! What's even worse is waiting for it to be repaired
for almost three weeks, when the problem is still there after the repair. What are they doing at the repair centers?! How about testing the console before shipping it... I hope they fix your problem, best of luck!

Usually they ship a refurbished console since it would take longer to repair a console and send it back. There's a warehouse in Kentucky that they ship from.