Hide Fiddler requests where the overall elapsed time was under 1 second.

HideFastRequests.js

//
// Click Rules > Customize Rules. Uncomment the *OnDone* function and update it with
// the code inside the function body below.
//

    // This function executes after Fiddler finishes processing a Session, regardless
    // of whether it succeeded or failed. Note that this typically runs AFTER the last
    // update of the Web Sessions UI listitem, so you must manually refresh the Session's
    // UI if you intend to change it.
    static function OnDone(oSession: Session) {
      // Hide any Session that took under 1 second.
      if ((oSession.Timers.ClientDoneResponse - oSession.Timers.ClientBeginRequest).TotalMilliseconds < 1000) {
        // oSession["ui-backcolor"] = "green";
        oSession["ui-hide"] = "fast!";
        oSession.RefreshUI();
      }
    }

If you’re trying to do an “After the fact” filter instead of one that runs at processing time, you’d do it like this, just inside the Handlers class

BindUIButton("Remove <1s")
ContextAction("Remove <1s")
public static function doRemoveFastSessions(arrSess: Session[]) {
	// If not running on a selection, apply to *ALL*
	if (arrSess.Length < 2) {
		arrSess = FiddlerApplication.UI.GetAllSessions(); 
	}
	for (var i: int=0; i<arrSess.Length; i++){
		var oSession = arrSess[i];
		if ((oSession.Timers.ClientDoneResponse - oSession.Timers.ClientBeginRequest).TotalMilliseconds < 1000) {
			oSession["ui-hide"] = "fast! put the word 'stealth' here to hide literally EVERYTHING, even errors, etc";
			oSession.RefreshUI();
		}
	}
}