Can I leave my cinnamon bars unbaked in the fridge for a few hours?
It will probably not affect taste, however, it will affect texture.  The reason is that the flour will react to the moisture in the batter and start to convert to gluten.  This will produce at best a chewier bar (which may actually be desirable) or, at worst, a rock hard bar.  

If you are willing to take this textural risk, then I would recommend putting the pan directly into the oven from the refrigerator.  This is because the bars will be so thin (and thereby have relatively large surface area) that they will come up to temperature in the oven quite quickly.  You may have to cook them slightly longer; just make sure to test them with a toothpick or, better yet, a thermometer before removing.  The internal temperature should be a little over 200°F or a little under 100°C.

If you want to minimize the risk of chewiness/hardness, do as little initial mixing of the flour with the batter as possible.  It is okay to have some small lumps of flour since they will absorb the batter during the resting time in the refrigerator.  This suggestion is due to the fact that gluten is formed both by moisture and mechanical agitation (mixing).

Another option, for which there is no potential harm, would be to mix the wet ingredients in advance and refrigerate them, also mix the dry ingredients in advance and leave them at room temperature, and then mix the wet with the dry just before putting everything into the oven.