There are few things missing to detect more buttons, i suggest you install the attached plugin, and in your plugin just use the following code :
PHP Code:
#include <amxmodx>
#define Start 0
#define Stop 1
forward client_use_button(id, iButtonType)
public plugin_init()
{
}
public client_use_button(id, iButtonType)
{
if( iButtonType == Stop )
{
// stop timer here
}
else
{
// start timer here
}
}