Refunds

How much time can a refund take to post to the customer's account?

The Square full refund time frame typically takes 2-7 business days.
Once the refund is processed and sent to your customer's card issuing bank, it can take another 2-7 business days (depending on the bank's processing speeds) for the refund to post to the customer's account.

Payments processed on Square Online are only eligible to refund within one year.

Source:  Refund Overview | Square Support Center - US (squareup.com)

NOTE: Refunds in Square will say "Pending Refund" after you have issued them, this can lead you to think it has not gone through, however, rest assured, the refund has gone through correctly. The refund requests always remain in Pending status for a few hours.