Should I Amend Now Or Later? Forgot a 1099R.

I filed my taxes a few days ago and today I received another 1099R from where my old 401K closed out my account with them and sent me a check in the mail (I completely forgot about this -- it was in early January of last year). The check itself was only for $46 and the tax withheld was about $9. My question is, should I immediately amend my return on 2/8 when the amendment forms are available? Or wait and file after my initial refund is processed? If I amend on 2/8, would I still receive my refund on the same schedule or will it be prolonged 21 days from 2/8?

I really need my refund money asap, so I'm hesitant to do anything that would delay it if I can just file the amendment afterward (and pay the IRS whatever little penalty is attached from the "involuntary early withdrawal").