A researcher hired by NASA to find a wormhole during an alien invasion.

There is a limitation.

Isn't it a little superfluous to say from outer space? Where else would an alien invasion come from?

And why does he only have seven days to do it if he has a time machine? Or is there some limitation that only allows him to travel seven days into the past? I remember seeing a few episodes of a short-lived TV show with the premise that they always sent him seven days into the past.