using System;
using System.Text.RegularExpressions;
using System.Linq;

public class Test
{
	public static void Main()
	{
        var str = "hello Exclude1 4:32  test test Exclude2 5:23 hello 2:19 some more text 42:3 more text";
        var matches = Regex.Matches(str, @"(?<!Exclude1 )(?<!Exclude2 )\d+:\d+");
        foreach (var match in matches.Cast<Match>())
            Console.WriteLine(match.Value);
	}
}