Is 945 half past nine quarter to ten quarter past ten or a quarter past nine?

945 . would be written as ' 9;45 '

It means forty five minutes PAST the hour of 9 o'clock.

Since the hour is divided into 'quarters' of 15 minutes each, it would leave 15 minutes (one quarter) to reach 10 o'clock. So would be expressed as 'Quarter to Ten'.

Similarly.

915 = 9:15 *