how to break JSON data into substring so it can be used for later calculation?

I have been stuck at this problem for a couple of days and couldn't figure it out.

Below is the data I have:

    body = {
      columns: {
        links: [
          "link1 ,\nlink2\n",
          "link3 ,\nlink4\n"
        ],
        timestamps: [
          "[2:00-4:30, 5:53-7:23],\n[15:15-16:16, 45:43-47:32, 1:02:30-1:03:45]",
          "[1:00-3:20, 8:50-9:20],\n[18:50-19:30, 42:00-46:28, 1:05:31-1:08:00]"
        ]
      }
    };

The timestamps for link1 would be 2:00-4:30 and 5:53-7:23, timestamps for link2 would be 15:15-16:16, 45:43-47:32, 1:02:30-1:03:45, however, they are in one string, same case with "link1, link2\n"

What I intended to do is as follow

For example:

body["columns"]["timestamps"][0]  // "[2:00-4:30, 5:00-7:00],\n[15:15-16:16, 45:43-47:32, 1:02:30-1:03:45]"

timestamp_group = body["columns"][timestamps][0].match(/(?<=\[)(.*?)(?=\])/g)[0]  // "[2:00-4:30, 5:00-7:00]"

//by using timestamp_group.split('-')
timestamp_group[] // ["2:00-4:30", "5:00-7:00"]

//further split into ["2:00", "4:30"]

//then using hmsToSecondsOnly() to make it into [120,270]

function hmsToSecondsOnly(str) {
    var p = str.split(':'),
        s = 0, m = 1;

    while (p.length > 0) {
        s += m * parseInt(p.pop(), 10);
        m *= 60;
    }

    return s;
}

It would be something like this in the end:

   [[120,270],[300, 420]],[[,],[,],[,]]

Then I can map links to time stamps.

body["columns"]["links"][0][0] to body["columns"]["timestamps"][0][0]

and calculate their durations.

I want to avoid using too much nested for loops, is there any better(elegant) way to approach this? Thanks.

I am not sure how to loop them properly. if using forEach, how should i start(nested or recursive?) Here are the attempts I tried in console.

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