- As of this morning, he was not in support of the motion.
- As at this morning, he was not in support of the motion.
Which is correct?
AS of: Used to indicate the time or date from which something starts:
Your second sentence is wrong.
I suppose both are correct. I have heard both used by native English speakers. I prefer the first to the second but that is probably because I am English and the second sentence sounds American, or at any rate not British.
"As at" is mostly used in stats and finance. It indicates a bi-temporal slice of data and thus has two time references buried in it. It really translates to "as of a certain time, I knew something about some other time."
For example, let's say that on Jan 1 I had $20 in my bank account, and project it to be $25 on Feb 1. Let's now say that on Jan 2 you found out it would still be $20 on Feb 1.
You would say that as at Jan 1 my bank account is projected to be $25. As at Jan 2, my account is projected to be $20.
As of Jan 1, however, I only have $20.
I agree, it sounds odd, but it does have a limited purpose.