It will not be long before 和it was not long before 有什么区别

It will not be long before 和it was not long before 有什么区别
比如_________________the baby elephant can walk.(be)
不就小象就会走路了.
为什么要用 It will not be long before.
注意我的疑问再long前面的那个“be”上,而不是时态.加不加“be”有什么区别吗~