Parse the string "26h44m3s" to TimeSpan in C#

You can use Noda Time for this, parsing as a Duration. You could then convert it to a TimeSpan - or you could use Noda Time everywhere and have a nicer experience :)

Sample code:

using System;
using NodaTime;
using NodaTime.Text;

class Program
{
    static void Main()
    {
        string text = "26h44m3s";
        var pattern = DurationPattern.CreateWithInvariantCulture("H'h'm'm's's'");
        var duration = pattern.Parse(text).Value;
        Console.WriteLine(duration);
        var ts = duration.ToTimeSpan();
        Console.WriteLine(ts);
    }
}

If you have multiple patterns that need to match, you can create a composite pattern - although you'll need to list all the patterns explicitly. Here's an example of that:

using System;
using System.Linq;
using NodaTime;
using NodaTime.Text;

class Program
{
    static void Main()
    {

        string[] formats =
        {
            "H'h'm'm's's'", "H'h'm'm'", "M'm's's'", "H'h'", "M'm'", "S's'"
        };
        var patterns = formats.Select(DurationPattern.CreateWithInvariantCulture);
        var builder = new CompositePatternBuilder<Duration>();
        foreach (var pattern in patterns)
        {            
            // The second parameter is used to choose which pattern is
            // used for formatting. Let's ignore it for now.
            builder.Add(pattern, _ => true);
        }
        var composite = builder.Build();


        string[] values = { "26h8m", "26h", "15s", "56m47s" };
        foreach (var value in values)
        {
            Console.WriteLine(composite.Parse(value).Value);
        }
    }
}