23:23 UTC - twenty-three twenty-three UTC

Clock	Time	Spoken
24-hour clock	23:23	twenty-three twenty-three, twenty-three minutes past twenty-three, thirty-seven minutes to midnight, thirty-seven minutes to zero
12-hour clock	11:23 PM	eleven twenty-three pm, twenty-three minutes past eleven pm, thirty-seven minutes to midnight, thirty-seven minutes to twelve am
Military	2323Z	two-three-two-three hours, twenty-three twenty-three 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.