using System;

using System.Collections.Generic;

​

 var data = new List<string> {

    "2021-08-26 19:46:10",

    "2021-08-26 19:46:32",

    "2021-08-26 19:47:45",

    "2021-08-26 19:48:09",

    "2021-08-26 19:50:10",

};

​

var resultData = new List<ResultDatum>();

var timeout = TimeSpan.FromMinutes(2);

​

foreach (var datum in data) {

    var time = DateTime.Parse(datum);

    if (resultData.Count == 0

       || time - resultData[^1].EndTime > timeout) {

        resultData.Add(new(time, time, 1));

    } else {

        resultData[^1] = resultData[^1] with {

            EndTime = time,

            Frequency = resultData[^1].Frequency + 1

        };

    }

}

​

foreach (var resultDatum in resultData) {

    Console.WriteLine(resultDatum);

}

​

record ResultDatum(DateTime StartTime, DateTime EndTime, int Frequency);

​