Hi!
For these, we can say:
12:37 = It's Twelve and thirty seven
R = Son las 12 y treinta y ciete
5:45 = It's Five and forty five
R = Es las Cinco y Cuarenta y cinco.
6:30 = It's Six and thirty
Another way = It's half past six
R = Son las seis y media.
4:23 = It's Four and twenty three
R = Son las cuatro y veintitrés
Cya!