Well, if you're trying to get the min-max range for only one object, and bake only that one object, your're going to have to determine the start and end for just that object (unless you always know that everything in the scene starts and ends on the same frame). Therefore, add this:
$startTime = findKeyframe -which first tracerLocator
;
$endTime = findKeyframe -which last tracerLocator
;
then modify this in your bakeResults command:
-t ($startTime+":"+$endTime);
otherwise, the simplest way (with all keys for all objects starting and ending on same frame) is:
setPlaybackRangeToMinMax;
bakeResults tracerLocator;