I need to avoid any movement in the tripod, so I want my camera to shoot 1 second after I press the button. How can I set it to shoot 1 second after I press the button? The choices available by default are 2 and 10 sec. How can I set it to 1 second?
You cannot. Use the 2s timer instead which solves another problem too.
The first shake occurs when you release the shutter which both 2s and 10s timers avoid. This is obviously the one you know about.
The second shake occurs from the mirror in the camera as it raises to take the shot. To avoid this, the mirror must be up when the timer starts. This is automatically done on the 2s or 3s timers on several DSLRs, including yours.
Use the Canon TC80N3 timer. You can do a lot more with that timer than a 1 second wait. You can do intervals, time lapse, etc. You can do bulb exposures longer than 30 seconds. I love mine!
Now, it has worked on many Canon DSLRs that I've seen, just don't know about the 550D. But google it some and see if it works for you.
Look at the MagicLantern alternative firmware : http://magiclantern.wikia.com/ It contains many usefull features. If delay shot is not there, you can ask them to add it.