For jelly roll, it would be a very bad idea to use a different sized pan unless you also adjust the size of the recipe. Jelly roll recipes usually make exactly the amount of batter needed for the size pan they call for and you can't stuff that amount of batter into a smaller pan, nor can you spread it out in a larger one and expect to get a cake that you'll be able to use in the finished product.
However, since jelly rolls only take 12-14 minutes to bake at the best of times, if you have the proper amount of batter for the size pan you're using, you're not going to have to adjust the time very much. Just watch toward the end (through the window, if possible, you don't want to keep opening the oven when baking a cake), and as soon as the cake pulls away from the edges, remove it.