英语表达时间的疑问,"It is half past ten" or "It is a half past ten"?

英语表达时间的疑问,"It is half past ten" or "It is a half past ten"?
“现在是10：30”应该是“It is half past ten”还是“It is a half past ten”?
我觉得应该是前者,今天一个老师说是后者,必须得有a,是这样吗,我半信半疑!