Now I am watching the movie, while showing the moview, I have encounted not understand discription.
What does 'make the most of the hours you have left, saxons' mean?
to make the most out of X - means to spend X wisely, use it fully for one's advantage, or enjoy it well (as it/those may be the last ones, or as there's no certainty on how long X would/may last)
Also, please see this reference:
to use or enjoy something as much as possible - We're only in Paris for a day so let's make the most of it.
Take note that the OP's sentence and the above italicised sentence have similar essence. There's limited time, enjoy it amap.
It means that the Saxons are going to die soon (presumably at the hands of the one who said this quotation), and that they should enjoy the short time remaining to them.
Or, as you might hear people say on the Internet, ungrammatically (but don't use this in conversation; people will have no idea what you mean): You have no chance to survive make your time.