MyTime calculation, C#

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//Calculate time value
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            MyTime timeIn = new MyTime(1f);
            timeIn = new MyTime("-0915");
            
            Console.WriteLine(timeIn.ToDouble());
            Console.WriteLine(timeIn.ConvertToHour(-300.25f));
            Console.WriteLine(timeIn.ConvertToDecimal("3015"));
        }
    }
    
    public class MyTime {
        double timeValue = 0f;
        
        public MyTime() : this(0f) {
        }
        
        public MyTime(double timeValue) {
            this.timeValue = timeValue;
        }
        
        public MyTime(string value) {
            this.timeValue = this.ConvertToDecimal(value);
        }
        
        public double ToDouble() {
           return this.timeValue;
        }
        
        public double ConvertToDecimal(string value) {
            string hour = "00";
            string minute = "00";
            Match match = Regex.Match(value, @"^-?(\d{2,}).?(\d{2})$");
            if (match.Success) {
                hour = match.Groups[1].Value;
                minute = match.Groups[2].Value;
            }
            double result = Convert.ToDouble(hour) + (Convert.ToDouble(minute) / 60f);
            if (value.StartsWith("-")) /* negative value */ {
                result *= -1f;
            }
            return result;
        }
        
        public string ConvertToHour(double value) {
            int hour = Convert.ToInt32(value);
            double minute = Math.Abs(value) - Math.Abs(hour);
            return string.Format("{0:00}{1:00}", hour, (minute * 60f));
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,12 sec, absolute running time: 0,16 sec, cpu time: 0,14 sec, average memory usage: 16 Mb, average nr of threads: 4