G'Day Ladies and Gents

I am trying to get the 70d to take 4 sec exposure on a timer or be able to turn it on and off

im trying to take photos of of fireworks as I'm doing the show I can't sit/stand manually and take the photos,

The camera is in the center of the area with me to show a different perspective of the shows.

not sure,maybe there is a program I can get to do it but not really wanting to have to much equipment in the middle

Bazza