Questions about hidden ball trick?

Today in my baseball game we attempted to pull a hidden ball trick. Runners on second and third with 1 out. The coach called time and called everyone to the mound. The ball got to the first baseman. Pitcher is on the mound and the first baseman tags the first base runner leading off first. According to the umpire it didn't count. He said that first that he didn't call time in and also the pitcher was on the mound. IS this true and can you quote the MLB official rules.