我xx点之后没课。

You can say我上学到xx点。or我到xx点下课。or我到xx点放学。

我要上学直到xx点钟。 I 我 have school 上学，上课， where have means 有，school means 学校， when combines together 'have school' in total it means 上学，上课 until 直到 9 o'clock 9点钟