This is the first time that I have used a flower nail in the center. Could that be the hold up?
What temp are you baking at?
What size pan are you baking?
How full do you have the pan?
How wet was the batter (a more liquidy batter takes longer to bake)?
The flower nail is supposed to have the cake bake faster in the middle. Without it, your edges would bake really quickly and the middle wouldn't be done.
So the nail shouldn't be slowing the speed down. I agree with Pterrell about the liquidity of the cake. Some of my cakes take a really long time to bake because the cake batter is like juice (only a little thicker).