To say the time, it would be "son las seis for example. 30 minutes is "medio" and 15 minutes after is "cuatro". However, when it goes above medio, you would have to say "son las seis menos veinte" (5:40). If you were using number and hours, you would use hora for "una hora" or "horas" for any number greater than 1. Sorry if this didn't help.
