Look in skin/common_files/js/ajax.add2cart.js and find the code you inserted when installing the mod
If you find in it
Code:
onComplete: function(){ setTimeout($.fn.colorbox.close,5000); },
it auto closes after 5 seconds. If you want to disable it just change it to
if you want to increase the auto close time change 5000 to whatever number you want, for example 10 sec will be 10000