SAS If conditional before PROC SORT

if &var. not in ('quarter' 'period' 'year') then do;
    proc sort data=test_&var.;
        by descending column1;
    run;
end;

I'm trying to attach a conditional statement before a proc sort statement, but I'm having trouble getting the IF to work outside of a data step. Is there some way around this?

Basically I don't want to sort any test_&var. datasets that contain a time variable as those are the only datasets I want to retain a particular sequence in.