Is 我五分钟后就回来 ambiguous out of context? My newsletter says this sentence


  我五分钟后就回来。


is translated as "I'll be back in 5 minutes".

I am curious to know whether this sentence could be translated as "I came back 5 minutes ago", or does it need to be changed? If so, how and why?
"I'll be back in 5 minutes" is the only correct translation for this sentence. 

"I came back 5 minutes ago" is 


  我5分钟前就回来了。