When making soda bread, 45 min on baking sheet or 15 min on cast iron skillet?
If you read some of the reviews on the one that says to bake for 45 minutes (Brennan's), many of them say it was done in less time:

sunnieday:


  Really great and simple recipe. Recommended cook time is too long. I cooked mine for about 25 minutes and it was perfect. Will use this again. 


Nutmeg~n~Pepper


  After making as written and baking for the stated time, I find it hard to review how the bread tastes as it comes out way overcooked and rubbery.


lambertfan


  I did follow the advice of another review post with only baking for 30 min. 


So it looks like the bake time on Brennan's recipe is too long.

As to the pan vs sheet, with the sides of the pan so close to the loaf, it can certainly absorb and radiate some extra heat to the bread, so that might explain a little of the time difference... but not 30 minutes worth... but since the actual bake time for the sheet loaf is really 25-30 minutes, that might account for it... but the skillet would also take longer to heat up initially (assuming it's not preheated), so it would probably make the bottom of the bread cook more slowly.

So, as always with baking, don't bake by time. Keep an eye on your baking and pull it when it's done, not when the time is up.