"今晚8点" 的英语表达是 "eight o'clock tonight"。
"tonight" 是英语中表示“今晚”的词，来源于古英语中的 "niht"，意思是“晚上”。
"eight o'clock" 是表示“8点钟”的词组，"o'clock" 来源于中世纪的 "of the clock"，意思是“钟点”。
一些例句：
I'll see you at eight o'clock tonight. (我今晚8点见你)
Don't forget our meeting is scheduled for eight o'clock tonight. (别忘了我们今晚8点有会议)
I'm going to bed early tonight so I can wake up at eight o'clock. (我今晚早点睡，明天8点醒)