My uncle died in Georgia 16 months ago. As a an heir am I to receive an accounting of the assets? If so, is there a timeline requirement?

When a Will is submitted for probate (proving), it becomes a public document.  Check with the clerk of the probate court where your uncle lived and died.  Note also that (1) Wills name as beneficiaries whomever the person writing the Will wants and (2) you are an heir only if there is no Will and only if your uncle left no spouse, no children, no parents and no siblings.