How long should i wait if my employer deposited severance pay into my account that i'm supposedly not entitled to?

I was told in July that I was being laid off and that I had 60 days. I was entitled to severance pay but only if I worked the full rest of the time until my last day. I did not, I got another job and had to take it, and left a month before my last day. When I left they reiterated that I was forfeiting my severance which I knew. However, this past Friday was what would have been my last day and on that day they direct deposited what I am assuming to be my severance with taxes already taken out. I figured they would turn around and take it back out, which I really don't understand why they would even take the time to put it in anyway, but it's still there. Is this a common practice? I'm not going to use the money but I am not sure how long I need to wait or if there is a statute of limitations on how long they can come back on me for the money if it stays in there.