Так что это просто javascript.
Если строка времени всегда будет выглядеть одинаково, вы можете сделать:
let times = ["03:30:00", "01:45:00", "00:15:00"]; // you can have an unlimited number of time strings
let hours = 0;
let minutes = 0;
let seconds = 0;
for (const i in times) {
const time = times[i];
let splitTime = (time + "").split(":"); // make sure it's a string
seconds += parseInt(splitTime[2]);
if(seconds > 59){ // make sure it only goes until 59
minutes++;
seconds = seconds % 60;
}
minutes += parseInt(splitTime[1]);
if(minutes > 59){ // make sure it only goes until 59
hours++;
minutes = minutes % 60;
}
hours += parseInt(splitTime[0]);
}
let totalTime = (hours < 10 ? "0" + hours : hours) + ":"
+ (minutes < 10 ? "0" + minutes : minutes) + ":"
+ (seconds < 10 ? "0" + seconds : seconds); // put the left side zeros