what is the meaning of the latter part of the sentence?
Writing on a forum loosely related to running your business may be considered work, but it’s hard to see how chiming in on old topics stacked against his urgent goal to ship his product on time.
what is the meaning of "how chiming in on old topics stacked against his urgent goal to ship his product on time.
"?Thx.

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Answer

This is quite unusual. In this context, chiming in would mean joining in or adding his comments to a forum thread. So the remark means....is it best use of his time to be commenting on old topics on a forum instead of working to ship his product on time. He would rather 'play' on the internet than do his job :)

Answer

Chiming in - joining in on something, a conversation for example. 
The writer was saying that the person was spending too much time writing on old topics. This did not help his business. Shipping products to customers is more important.