The time is now 能不能作为一个单独的句子 译为 时间就是现在

当然可以。

参见纽约时报：

/2009/03/29/arts/design/29ouro.html?pagewanted=all&_r=0

具体译法须参考语境，上面的例子可以译为「就是现在」。

也可以强调Now，将其提前，如MLK.Jr（小马丁路德金)的Dream Speech中有如下一段：

Now is the time to make real the promises of democracy;

now is the time to rise from the dark and desolate valley of segregation to the sunlit path of racial justice;

now is the time to lift our nation from the quicksands of racial injustice to the solid rock of brotherhood;

now is the time to make justice a reality for all God’s children.