I'd like to make sodium carbonate for ramen noodles. The instructions on the web however vary greatly. One source says to bake baking soda at 350 degrees for 2-5 hours. Others say 250 degrees for an hour. Another says just 200 degrees for an hour.  Does the temperature even matter at all?   How about if I use a higher temperature like 450 degrees? This would be preferable for me as I only need a small amount and I can probably bake it at the same time I'm baking bread. 
160 °C  (320 °F) for 1-2 h worked for me once, but higher temperatures should not hurt the process.   If you are starting with dry sodium hydrogen carbonate, the mass should reduce to 63 % of the starting mass (more reduction in case of wet starting material).  Explanation for the mass loss number: You are converting two equivalents of sodium hydrogen carbonate with a molar mass of 84.01 g/mol to one equivalent of sodium carbonate with a molar mass of 105.99 g/mol. 105.99/(2*84.01) = 63 % 