nah it woulda happened like this...
clark could only go to the future cause that ring was programmed to head forward to the time where the legion would be. in this time he spends in the future fighting alongside the legion but eventually he has to head back and set things right. but before he does that Brainac 5 has to wipe his memory of wut he learned in the future cause thats just something that has to be done. And boom he's back two days before all he left.
this is all explained in that cartoon Legion of Superheroes.... come on guys catch up.
Oh yeah... and how the hell do you pass up a chance to kill TORI SPELLING... damnit CLARK.. "if your gonna step up to the bell you might as well ring it"
(kudos points for who gets where that quotes from, show and name... hint: it is a fairly recent episode)