Timer lag at GUIText drawing.

Hello!
I write game with forward timer in format 00:00:00 (min:sec:milisec)
But on first execution of timer ticking i have annoying lag in ~1 sec. This happens only on fisrt level. On second (and other levels) everything just fine. More over: if i pressed “replay” button (without closing game) there is no any lag. BUT if i close my game and start again this lag appearse again. After long time of debugging i figure out, than lag in this row:

gtScoreCount.text = string.Format("{0:00}:{1:00}:{2:00}", minutesDisplay, secondsDisplay, nanoDisplay);

I tried move this to InvokeRepeating() (instead of Update() ), tried change GUIText on Uniti.UI.Text. but have no any positive result. This driving me crazy. Can u advice me what i doing wrong? . Here is my full code now:

public class TheTimer : MonoBehaviour {

    public static float timerGlobal;  //global levels timer
    public GUIText gtScoreCount;
    public bool timeStarted;
    public  float timer;  //local level timer
    private float timerDisplay;
    private float minutesDisplay = 0;
    private float secondsDisplay = 0;
    private float nanoDisplay    = 0;


    void ResfreshTimer(){

        if (timeStarted) {
            // IF COMMENT THIS STRING EVERYTHING GO FINE WITHOUT LAG
            gtScoreCount.text = string.Format("{0:00}:{1:00}:{2:00}", minutesDisplay, secondsDisplay, nanoDisplay);
        }
    }

    void Update(){
        if (timeStarted) { //global ticking timer
             timer += Time.deltaTime;
            timerDisplay = timer + timerGlobal; 
            minutesDisplay = Mathf.Floor(timerDisplay / 60);//.ToString("00");
            secondsDisplay = Mathf.Floor(timerDisplay % 60);//.ToString("00");
            nanoDisplay    = Mathf.Floor(timerDisplay * 100 % 100);//.ToString("00");
    }

    void Start () {
        timeStarted = true;
        InvokeRepeating("ResfreshTimer",7.0F,0.05F);
    }

}

Holy waka vaca. I solved this. I’ll answer to myself. Maybe somebody this helps.

This was really deep. And it was… font renderer problem.
My FONT was imported as “dynamic” and on 1st lvl I forced GUIText to render all sybols from 1 to 9 in one frame (milisec timer). I solved this by putting gameobject with GUIText " 123456789:’ ", fontsize 30, color - white (used in my game - it is important) on hidden (unreached by camera X,Y) area of my Logo-scene.

Now it works perfectly.