I've been tinkering with material that focuses on the Adirondack Mountains of upstate NY during the 1890s. Would that be feasible? Or should I focus on a more contemporary era that possibly draws from the history I have envisioned?

Liminal Horror defaults to "modern horror", which is really anything from around the 70's until now, so typically it's expected that entries will fall under that category. However, I'm not particularly concerned with making that a firm mandate if you've got a cool idea that you're excited to write. Just make it clear that it's not set in the standard timeframe. Maybe someone could even use it as a prologue or flashback sequence in their games.