How to make for loops run faster - Psychtoolbox in matlab

Question

I created a MATLAB code using Psychtoolbox to make an experiment. Everything works as I intended but it seems the initial loading of the experiment takes too long. The task is a simple yes/no response task whether the target word('probe') appeared in the previous set of word stimuli.

I put basic intro text as an image and then wait for any keypress to start the experiment but it will take about 40 seconds to actually begin the first trial after any keystroke. I want to make it work without any delay. It should start its first trial immediately after any keystroke.

I checked the timestops with GetSecs() on numerous positions in the code and it was not anything to do with loading stimuli or initial setting of the experiment before the for loop I attached below.

To make things look simpler, I changed some of the variables into actual numbers I used. I can gurantee that it is not due to large stimuli size since it is only 1500 words. Once the for loop starts, it goes smoothly but it takes 40 seconds to actually start the first trial so I think it is something to do with a specific function in the for loop or the way I built it.

Please let me know if anything is too vague or unclear. I will do my best to make things read better.

Edit: I minimalized the code leaving only the function names used in Psychtoolbox. I left the functions I used in between loops to let you know if they could cause any delay. It will not be possible to run this without Psychtoolbox installed so I guess you can briefly examine the structure of the code.

for trial = 1:250
    for i = 1:6 
        DrawFormattedText();
        Screen();
        WaitSecs(0.5);
    end
    DrawFormattedText();      
    flipTime = Screen();
    WaitSecs(0.5);
    DrawFormattedText();
    flipTime = Screen();
    rt = 0;
    resp = 0;
        while GetSecs - flipTime < 3
            clear keyCode;
            RestrictKeysForKbCheck();
            [keyIsDown,secs,keyCode] = KbCheck;
            respTime = GetSecs;
            pressedKeys = find(keyCode);
            % ESC key quits the experiment
            if keyCode(KbName('ESCAPE')) == 1
                clear all
                close all
                sca
                return
            end
            % Check for response keys
            if ~isempty(pressedKeys)
                for i = 1:2
                    if KbName(i) == pressedKeys(1)
                        resp = i;
                        rt = respTime - flipTime;
                    end
                end
            end
            % Exit loop once a response is recorded
            if rt > 0
                break;
            end
        end
    if rt == 0 || rt > 3 % 3 second limit for subjects to react to the probe stimuli
       DrawFormattedText(); 
       Screen();
       WaitSecs(1);
    end
    Screen();
    vbl = Screen();
    WaitSecs(1);
    % Record the trial data into output data matrix
    respMat{1, trial} = trial;
    respMat{2, trial} = resp;
    respMat{3, trial} = rt;
end