It's not that bad, good little time waster...but there are some flaws:
First off, you're an assassin from the future and your job is to kill the intended target...why then after you kill them do you NOT hide the body AND leave a trail of bloody footprints to boot? Any assassin who knows anything about the killing business knows to hide the body and NEVER leave any evidence. Get in, make the kill, get out. No witnesses, no nothing; it's Assassination 101.
Second you're an ASSASSIN, killing is your stock in trade and you can't kill the guards?!? I know you have the Super Speed and Invisibility powers but still even if you could just knock the guards out it would be better than doing nothing.
Also why the timer? If everything is random like the movement of the guards and target why not give the player an unlimited amount of time just in case all the guards decide to gather around the exit portal--I had that happen when I played this and my time ran out.
It's not bad, I liked it, but I think a few little tweaks and it could be better.