soon after 不久之后, 稍后,after是连词,后面跟一个句子.
before long
是“很快,不久”的意思, 可以用于各种时态.是词组表示时间,单独用.
例如:
1).I'll see the film before long 我不久就要看这部电影.
2)."Before long, the noise dropped completely and the boat began to drift gently across the water."
"不久,轰鸣声完全消失了,于是这只船开始慢悠悠地漂浮在水面上."