One time, three ways to write it
2:30 PM, 14:30, and 1430 describe the same time of day. Choose the format you have and the format you want, then enter your time. The result keeps the minutes unchanged.
Converting by hand
For afternoon and evening times from 1 PM through 11 PM, add 12 to the hour. So 7:45 PM becomes 19:45, or 1945. Morning hours stay the same, with a leading zero when needed. The exceptions are 12 AM, which uses hour 00, and 12 PM, which uses hour 12.
For an important schedule, write noon or midnight and the date when ambiguity matters. NIST explains the noon and midnight conventions, including why 0000 and 2400 can refer to different date boundaries.
To find the time between two clock readings, use the Hours calculator.