Nepal is 5 hours 45 munities ahead (+5:45) of GMT (Greenwich Mean Time). Nepal, India and Sri Lanka all are lie in nearly same longitudinal line. But still Nepal time is 15 munities difference with India, whereas Sri Lanka doesn't.
Mt Gaurishanker is Nepali timeline standard, it situated in Dolakha Districts. While traveling in Nepal through the India, you need to fix your watch Nepali Time. Some time you might be confused.