I say 'new' Action Comics #1 as I'm not referring to the one published in the 1930's, but rather the one that was released on Sept 7, 2011. In this issue, we see an extremely young Clark Kent. As Superman, he can't fly, and his powers are weaker than the old Superman. His outfit doesn't match the outfit from the cover of the new Justice League #1 either. So it seems like Action Comics #1 is a flashback, like Justice League #1, but there's no 'X years ago' at the start of Action Comics #1 like there is at the start of Justice League #1, so I assumed it was in the present. Has DC stated when this comic occurs in the new continuity?
This article on Comics Alliance has this Grant Morrison quote:
And I wanted to do a story of Superman's first year in Metropolis when he wasn't so powerful and he was a bit more of a liberal activist.
This is somewhat confusing because Justice League also takes place five years in the past and features a much more capable (and costumed) Superman. I'm not finding much official word past interviews with Grant Morrison and the general understanding that Action Comics takes place before Justice League which takes place before anything set in the "present." However, this issue is being discussed over at Comic Book Resources, and user bulldog_milt hypothesizes:
Action Comics #1 occurs 6 months to 1 year before Justice League #1, Justice League #1 occurs 5 years before the other titles...