I just noticed that some forum posts are showing future times for me, but haven't been able to find where I can change this.
the site is set to EST (GMT -5), there's no way to customize this setting unfortunately
Subeta is based in EST/-5GMT, meaning all events, updates and such will be in this time. It isn't something we can adjust because, in the sense of updates, event starts and the like, it's good to know exactly what time in site terms. Like monthly collection releases are almost always around 3PM EST.
I get it's confusing but we legit have clocks on our computers and phones that will do multiple time zones. Having that displayed somewhere might help?

As others have said, the site is set to Eastern United States time, and there's no way to change the way forum posts display time. If you want to know what the current time is on the site, there is a site clock next to the "Toggle Sidebar" button. It's a bit small, but it should show the current site time!