At 4 o'clock.
The four friends program
I need my 4 o'clock coffee
If you mean 'half past four' (the time): 'las cuatro y media' If you mean 'half of four' (i.e. 50% of 4, i.e. 2); 'la/una mitad de cuatro' If you mean (as in American English) '3.30': 'las tres y media'
4:30
If you mean the time: las cuatro y cuarto If you mean simply the numbers: cuatro, quince.
If you mean 'half past four' (the time): 'las cuatro y media' If you mean 'half of four' (i.e. 50% of 4, i.e. 2); 'la/una mitad de cuatro' If you mean (as in American English) '3.30': 'las tres y media'
"Y cuatro" translates to "and four" in English.
"Cuatro dias" means four days in English.
It is 4:15 (cuatro = 4 cuarto = 1/4 = 15)
Cuatro punto cero cero OR, if you mean 4 o'clock - las cuatro
You most likely meant to ask: "What does son las cuatro menos cuarto mean?" which would translate to "It is 3:45." What you actually asked would translate to "It is a quarter minus a quarter."
Four hundred in Spanish is "cuatrocientos".