using System;
using System.Linq;
using System.Collections.Generic;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
    var groups = new Dictionary<string, string>
    {
        { "month", @"(JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC)" },
        { "day", @"\d+" },
        { "hour", @"\d+" },
        { "the_rest", @".*" },
    };
 
    var format = "{month} {day} {hour}:{the_rest}";
    var result = Regex.Replace(format, @"\{(\w+)\}", m => groups[m.Groups[1].Value]);
 
    Console.WriteLine(result);
	}
}

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