Whether filed on paper or electronically, amended returns are like the food on your plate:  It's all going to the same place.  And the latest from IRS is that they are working now on amended returns filed last October.  (And that was before the election.)  So I would wait until after April 15, when you have more time and your client may find even more 1099's to bring you.  Also, you will know if there is any error correction on the original return.  The world is not going to come to an end if you rush to do this, but your health might be jeopardized. 

Here is where to find out IRS processing times:

https://www.irs.gov/help/processing-status-for-tax-forms