Yes it will show the original post date because thats when the Thread/Post was created. You will notice though at the bottom it will say "Last Edited Post ?/?/?". If you want to change the "Post Date" then make the very first post within the thread say "Do Not Post In This Thread", Then the next post have the actual list of your squads members. Every time you update on the 1st and 15th then make a new post and delete the last list.