How long does it usually take Steam Support to process a refund request?

A few days for the refund approval, and up to a week to receive your money back.

it just depends. It took me two days to get it approved and 5 days to get the money.

Both times I used it it took under 24 hours for approval. First time the money was held up for about a week, the second time I had it also within 24 hours.

I got a response within a few hours of submitting mine to tell me it wouldn't go through.

Few hours in my case. Don't try to contact support though, then it will take weeks.

Approx. 4-5 days, in my case it was 24 hours; request - approval - wallet refund.