It's all down to the music. There should be an obvious split beat which is where the chasse fits. Everything then falls into place around that.
Cha Cha music has that split on beat 4, so it goes 1,2,3,4&. This makes the last step of the chasse on beat 1, and we break forward or back on beat 2.
Cha Cha Cha music (note the extra cha) splits beat 3 thus 1,2,3&4 which puts the chasse at the end of the bar and the break now comes on beat 1.
This gives a rather flat interpretation, counting 1,2,cha-cha-cha
If you can find some real music and place more hip emphasis on the last step of the chasse you get a much more exciting dance, counted (1)2,3,cha-cha-ONE.