First you need to convert it to a TimeSpan:
string[] strTimeSpans = new[]{"00hr:00min:17sec","00hr:03min:18sec","00hr:05min:25sec","01hr:39min:44sec"};
TimeSpan[] timespans = strTimeSpans
    .Select(s => {
        var parts = s.Split(':');
        int hour = int.Parse(parts[0].Substring(0, 2));
        int min = int.Parse(parts[1].Substring(0, 2));
        int sec = int.Parse(parts[2].Substring(0, 2));
        return new TimeSpan(hour, min, sec);
    }).ToArray();
Then you can use this code to get a readable TimeSpan, i have added it to a method:
public static string GetReadableTimespan(TimeSpan ts)
{
    const int SECOND = 1;
    const int MINUTE = 60 * SECOND;
    const int HOUR = 60 * MINUTE;
    const int DAY = 24 * HOUR;
    const int MONTH = 30 * DAY;
    double delta = Math.Abs(ts.TotalSeconds);
    if (delta < 0)
    {
        return "not yet";
    }
    if (delta < 1 * MINUTE)
    {
        return ts.Seconds == 1 ? "one second ago" : ts.Seconds + " seconds ago";
    }
    if (delta < 2 * MINUTE)
    {
        return "a minute ago";
    }
    if (delta < 45 * MINUTE)
    {
        return ts.Minutes + " minutes ago";
    }
    if (delta < 90 * MINUTE)
    {
        return "an hour ago";
    }
    if (delta < 24 * HOUR)
    {
        return ts.Hours + " hours ago";
    }
    if (delta < 48 * HOUR)
    {
        return "yesterday";
    }
    if (delta < 30 * DAY)
    {
        return ts.Days + " days ago";
    }
    if (delta < 12 * MONTH)
    {
        int months = Convert.ToInt32(Math.Floor((double)ts.Days / 30));
        return months <= 1 ? "one month ago" : months + " months ago";
    }
    else
    {
        int years = Convert.ToInt32(Math.Floor((double)ts.Days / 365));
        return years <= 1 ? "one year ago" : years + " years ago";
    }
}
Now this....
foreach (TimeSpan ts in timespans)
    Console.WriteLine(GetReadableTimespan(ts));
outputs:
17 seconds ago
3 minutes ago
5 minutes ago
1 hours ago
Demo