The original whitepaper PDF has this record:
"/CreationDate(D:20090324113315-06'00')"
This suggests that his timezone was UTC-6.
https://en.wikipedia.org/wiki/UTC%E2%88%9206:00#/media/File:Timezones2008_UTC-6.png
Pretty narrow strip
Wikipedia quotes an analysis of his posts that puts him in either UTC-5 or UTC-6.
Besides the date, it also records that he used OpenOffice 2.4.
There is no guarantee that that is his actual timezone. It is possible that he changed his clock to further hide himself."/CreationDate(D:20090324113315-06'00')"
This suggests that his timezone was UTC-6.
https://en.wikipedia.org/wiki/UTC%E2%88%9206:00#/media/File:Timezones2008_UTC-6.png
Pretty narrow strip
Wikipedia quotes an analysis of his posts that puts him in either UTC-5 or UTC-6.
Besides the date, it also records that he used OpenOffice 2.4.
He also could have posted at odd hours do that people searching for him would be following a red herring.