12:37 am UTC - twenty-three minutes to one am UTC

Clock	Time	Spoken
12-hour clock	12:37 AM	twenty-three minutes to one am, twelve thirty-seven am, thirty-seven minutes past midnight, thirty-seven minutes past twelve am
24-hour clock	00:37	twenty-three minutes to one, zero thirty-seven, thirty-seven minutes past midnight, thirty-seven minutes past zero
Military	0037Z	zero-zero-three-seven hours, zero zero thirty-seven hours

AM or A.M. - latin ante meridiem, meaning before midday, PM or P.M. - latin post meridiem, meaning after midday. Letter 'Z' in military time indicates ZULU Time Zone which is equivalent to UTC.