The timer_1.1.exe file you have requested: Tools and Utilities / Map Tools / Halo: CE Timer v1.1 - 2.47mb is not available. Perhaps try browsing all files for the game Halo: Combat Evolved and upload any files you want to share or are missing. This is the only information we could locate:
You can change maps after the timer has started. Select the map via the drop-down or scroll-bar. It does not support PAL at this time.