using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        var start = TimeSpan.ParseExact("10:00", "hh\\:mm", CultureInfo.InvariantCulture);

        var finish = TimeSpan.ParseExact("1100", "hhmm", CultureInfo.InvariantCulture);

        Console.WriteLine("Start: " + start);

        Console.WriteLine("Finish: " + finish);

        var diff = finish - start;

        Console.WriteLine("Diff: " + diff);

        var adjustment = TimeSpan.FromTicks((long)(diff.Ticks * 0.25));

        Console.WriteLine("Adjustment: " + adjustment);

        var adjustedStart = start + adjustment;

        Console.WriteLine("AdjustedStart: " + adjustedStart);

    }

}