On my last SWU request, they appeared in my account within a couple hours. I was able to use them at that time, long before the email, but the DM phone agent said something about needing to get some redemption code somewhere on her computer as it didn't appear as usual since I had just requested the certs.

IIRC this was late afternoon to early evening and my email appeared pretty early the next morning, so it was definitely well under 24 hours.