TimeSpan to Custom string like HH:mm:ss

Just use the ToString(String format) method of TimeSpan, passing in the format you require.

https://msdn.microsoft.com/en-us/library/dd992632(v=vs.110).aspx

E.g.

var ts = TimeSpan.FromMinutes(10000);
var output = ts.ToString(@"hh\:mm\:ss");
Console.WriteLine(output);

Just use :

delta.ToString(); // 00:00:10

which does the trick for you (Fiddle)

Or try this:

var str = string.Format("{0:00}:{1:00}:{2:00}", delta.Hours, delta.Minutes, delta.Seconds);

You can build an extension method if you use it a lot:

public static class MyExtensions
{
    public static string ToCustomString(this TimeSpan span)
    {
        return string.Format("{0:00}:{1:00}:{2:00}", span.Hours, span.Minutes, span.Seconds);
    }
}

Usage:

string strSpan = delta.ToCustomString();

From MSDN

using System;

public class Class1
{
   public static void Main()
   {
      TimeSpan[] spans = { TimeSpan.Zero, new TimeSpan(-14, 0, 0, 0, 0), 
                           new TimeSpan(1, 2, 3), 
                           new TimeSpan(0, 0, 0, 0, 250), 
                           new TimeSpan(99, 23, 59, 59, 999),
                           new TimeSpan(3, 0, 0), 
                           new TimeSpan(0, 0, 0, 0, 25) };
      string[] fmts = { "c", "g", "G", @"hh\:mm\:ss", "%m' min.'" };
      foreach (TimeSpan span in spans)
      {
         foreach (string fmt in fmts)
            Console.WriteLine("{0}: {1}", fmt, span.ToString(fmt));

         Console.WriteLine();
      }
   }
}
// The example displays the following output:
//       c: 00:00:00
//       g: 0:00:00
//       G: 0:00:00:00.0000000
//       hh\:mm\:ss: 00:00:00
//       %m' min.': 0 min.
//       
//       c: -14.00:00:00
//       g: -14:0:00:00
//       G: -14:00:00:00.0000000
//       hh\:mm\:ss: 00:00:00
//       %m' min.': 0 min.
//       
//       c: 01:02:03
//       g: 1:02:03
//       G: 0:01:02:03.0000000
//       hh\:mm\:ss: 01:02:03
//       %m' min.': 2 min.
//       
//       c: 00:00:00.2500000
//       g: 0:00:00.25
//       G: 0:00:00:00.2500000
//       hh\:mm\:ss: 00:00:00
//       %m' min.': 0 min.
//       
//       c: 99.23:59:59.9990000
//       g: 99:23:59:59.999
//       G: 99:23:59:59.9990000
//       hh\:mm\:ss: 23:59:59
//       %m' min.': 59 min.
//       
//       c: 03:00:00
//       g: 3:00:00
//       G: 0:03:00:00.0000000
//       hh\:mm\:ss: 03:00:00
//       %m' min.': 0 min.
//       
//       c: 00:00:00.0250000
//       g: 0:00:00.025
//       G: 0:00:00:00.0250000
//       hh\:mm\:ss: 00:00:00
//       %m' min.': 0 min.

Also if you want a custom made,

public static class TimeSpanExt
{
  public static string ToStringMyFormat(this TimeSpan timeSpan)
  {
     return timeSpan.Days.ToString("00") + ":" + timeSpan.Hours.ToString("00") + ":" + timeSpan.Minutes.ToString("00") + ":" + timeSpan.Seconds.ToString("00") + ":" + timeSpan.Milliseconds.ToString("00");
  }
}