The params fields are grouped. They include language, editor, and timezone. You can't separate them. However, what you can do is use CSS to hide the others so only timezone is visible. This can be done for example with the below CSS.
Code:
#cbfr_userparam_0,
#cbfr_userparam_1,
#cbfr_userparam_2,
#cbfr_userparam_3,
#cbfr_userparam_4 {
display: none;
}
The above assumes you're using CB 1.8 on J2.5. I recommend using Firebug for Firefox to inspect the fields on registration for better review of its classes for styling.
krileon
