周一下午6点可以用英语说作 "Monday evening at 6 o'clock"。
其中"Monday" 是星期一的意思，"evening" 是晚上的意思，"at" 是在...的时候，"6 o'clock" 是6点钟。
举例：
"I will meet you on Monday evening at 6 o'clock." (我会在周一晚上6点见你。)
"The party starts on Monday evening at 6 o'clock." (聚会在周一晚上6点开始。)
"Don't forget our appointment on Monday evening at 6 o'clock." (别忘了我们在周一晚上6点的约会。)