[FG28_Kodiak]

This make no sense

            double initTime = 0.0;
            Timeout(initTime += 100, () =>
            {
                GamePlay.gpHUDLogCenter("German bomber attack on radar stations!");
                GamePlay.gpHUDLogCenter("Supply train headed to Boulogne and Calais!");
            });

you will only see the last message after 100sec

if you will see both you should change it into

            double initTime = 0.0;
            Timeout(initTime += 100, () =>
            {
                GamePlay.gpHUDLogCenter("German bomber attack on radar stations!");
            });
            Timeout(initTime += 10, () =>
            {
                GamePlay.gpHUDLogCenter("Supply train headed to Boulogne and Calais!");
            });

Now you get the first Message after 100sec and the other 10sec after the first.
(You should change the times of second messagepart also, to avoid that the latest message overrides an earlier.)

The rest is ok if you use
public override void OnTickGame()
{
on the beginning.

So your script should look like:

using System;
using System.Collections;
using System.Collections.Generic;
using maddox.game;
using maddox.game.world;

public class Mission : AMission
{

    public override void OnTickGame()
    {
        base.OnTickGame();


        if (Time.tickCounter() % 432000 == 21600) // 240 min repeat, 12 min delay.
        {
            GamePlay.gpPostMissionLoad("missions/channelv6/BM1/Practice1.mis");
            GamePlay.gpPostMissionLoad("missions/channelv6/Supply/bluetrain_C2h.mis");
            GamePlay.gpPostMissionLoad("missions/channelv6/Supply/bluetrain_B2h.mis");

            double initTime = 0.0;
            Timeout(initTime += 100, () =>
            {
                GamePlay.gpHUDLogCenter("German bomber attack on radar stations!");
            });
            Timeout(initTime += 10, () =>
            {
                GamePlay.gpHUDLogCenter("Supply train headed to Boulogne and Calais!");
            });
        }

        if (Time.tickCounter() % 432000 == 216000) // 240 min repeat, 120 min delay.
        {
            GamePlay.gpPostMissionLoad("missions/channelv6/BM1/Practice2.mis");
            GamePlay.gpPostMissionLoad("missions/channelv6/Supply/bluetrain_B2h.mis");
            GamePlay.gpPostMissionLoad("missions/channelv6/Supply/bluetrain_C2h.mis");

            double initTime = 0.0;
            Timeout(initTime += 100, () =>
            {
                GamePlay.gpHUDLogCenter("German bomber attack on airbases!");
            });
            Timeout(initTime += 10, () =>
            {
                GamePlay.gpHUDLogCenter("Supply train headed to Boulogne and Calais!");
            });
        }
    }
}

Hint: 30ticks are around 1second.
so 21600 ticks is around 12 min and not 5
and 216000 ticks are 120min