When the time is after the hour (up to 30 minutes) we say past. When it's before the hour (but after 30 minutes past) we say to. We often use descriptions such as 'quarter past' and 'half past' to ...

Telling the time in Spanish. What time is it ... Son las dos y media - it’s half past two. Son las tres menos cuarto - it’s quarter to three. But that could be three in the afternoon ...