Why did Allah promise Moses forty nights, and when was that promise—was it before or after his people worshipped the calf?

Allah met with Moses for thirty nights, which He then completed with ten, making forty nights in total. This was so that the Torah, containing religious laws and doctrines, could be revealed to him. This event occurred after Allah had saved the Children of Israel from servitude, and before they worshipped the calf, which they had taken as a god in Moses' absence. When Moses returned to them, he found them worshipping it.