get (-) when i try too input the value for my input type="time"

let startTime = document.getElementById("startTime");
let endTime = document.getElementById("endTime");
let totalTime = document.getElementById("totalTime");

function CalculateTotalTime() {
    //console.log(startTime.value + " " + endTime.value);
    //console.log("totaltime: " + totalTime.value);

    const startTimeParts = startTime.value.split(":");
    const startHours = parseInt(startTimeParts[0]);
    const startMinutes = parseInt(startTimeParts[1]);
    console.log("Hours:" + " " + startHours + " " + "Minutes: " + startMinutes);

    const endTimeParts = endTime.value.split(":");
    const endHours = parseInt(endTimeParts[0]);
    const endMinutes = parseInt(endTimeParts[1]);
    console.log("Hours:" + " " + endHours + " " + "Minutes: " + endMinutes);

    const calculatedHours = endHours - startHours;
    const calculatedMinutes = endMinutes - startMinutes;
    const formattedTime = `${calculatedHours.toString().padStart(2, '0')}:${calculatedMinutes.toString().padStart(2, '0')}`;
    totalTime.value = formattedTime;
}

// Add event listeners to the input elements to calculate the time difference
startTime.addEventListener("input", CalculateTotalTime);
endTime.addEventListener("input", CalculateTotalTime);
totalTime.addEventListener("input", CalculateTotalTime);