Statins are usually taken before going to sleep. This is because the hepatic synthetic activity is maximum at night. Hence statins have maximum efficiency in decreasing cholesterol when given at night. This is especially important in statins with short half life such as simvastatin. Newer statins like atorvastatin have a longer half life.
Other drugs which block the hepatic synthetic function (eg: warfarin which blocks hepatic synthesis of clotting factors) are also best given at night time.