The fancomics section is highly moderated, since during the heyday of the forums fancomics used to be quite numerous and needed constant vetting. As the stickied guidelines thread suggests, all threads created here require moderator approval to appear, and at least one comic in the main post to start off.
Historically approval has taken anywhere from a couple days to several weeks, and I assume that depends on moderator workload behind the scenes. The subforum isn't anywhere near as active as it used to be and I suspect these things sometimes slip through the cracks. If you're really concerned about it like I was, I was told to message one of the subforum mods about it, which did the trick for me.