How long it takes for steam to provide you with refund?

Steam wallet refunds take around an hour, sometimes maybe more to get approved, however after they've been approved, they appear as "Pending" in your steam wallet, when you go into your steam wallet and then you'll go into account details you can see the estimated time when your balance will be available to spend.
Credit card or any other refund methods may take even to 5-7 business days, depending on what payment method you have used when buying the game/DLC, but most of the times it's 5-7 business days.

(Please note that refunds can be requested only if you have less than 2 hours of playtime in that game and you have bough that no longer than 2 weeks ago.)