that command 'wait' represents is having a script pause for one game tick of time. Usefull if you want a time gap between commands. You're probly refering to the fast forward script I use in video making which lets you use higher cl_avidemo numbers without hitting the screenshot limit. An example would be:
demo <demo name>;timescale 100;wait 40;timescale 1;cl_avidemo 60
If you tweak the amount of waits you can fast forward a certain amount into the demo and then have it start recording later. Anyway, hope this helps. I'm gonna try to edit the first post here to include everything in a guide shinyiu and I wrote about video making.