it wasn't long before i found a job.---before后接过去时.表示我没花多少时间就找到了工作.
it won't be long before our contry becomes a developed country._____before 后接现在时.表示我们国家很快就会成为一个发达国家.

过去式和将来式的区别
It wasn't long before that he came back
It won't be long before that he comes back

第一句是不久以前
第二句是不会很久