(one's) finest hour
The moment or time of one's greatest success or achievement. The team's come-from-behind victory in the semi-finals proved to be their finest hour.
your finest hour
the time of your greatest success. 1940 W. S. Churchill Speech to House of Commons Let us therefore brace ourselves to that duty, and so bear ourselves that, if the British Commonwealth and its Empire lasts for a thousand years, men will still say, ‘This was their finest hour’.