My Halo CE program take a long time to start
When Halo Custom Edition starts it performs a checksum calculation on all maps in the map folder. The map folder is usually located at C:\Program Files\Microsoft Games\Halo Custom Edition\maps.

Halo CE does this to verify that the map in your folder is the same as the map on the server you are going to connect to. The more maps you have in your C:\Program Files\Microsoft Games\Halo Custom Edition\maps folder the longer it takes for Halo CE to start.

To speed up the starting time create a subfolder to the C:\Program Files\Microsoft Games\Halo Custom Edition\maps folder called "hold"
C:\Program Files\Microsoft Games\Halo Custom Edition\maps\hold and drag all the maps you don't use often to that folder.

If you decide you want to play that map on a server then drag it back into the C:\Program Files\Microsoft Games\Halo Custom Edition\maps folder and re-start Halo CE.

NOTE: Once Halo CE is started it will not see any new maps you place in the \maps folder. In order to get Halo CE to see the new map you will need to restart the game.