[FG28_Kodiak]

You can do this via script:

Set your Airgroups on Idle.

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


public class Mission : AMission
{

    public void SetAirgroupActivAfter(Dictionary<string, double> StartAirgroupAfterTime)
        {
            List<AiAirGroup> allAirgroups = new List<AiAirGroup>();

            if (gamePlay.gpAirGroups(1) != null)
                allAirgroups.AddRange(gamePlay.gpAirGroups(1));
            if (gamePlay.gpAirGroups(2) != null)
                allAirgroups.AddRange(gamePlay.gpAirGroups(2));

            allAirgroups.ForEach(item =>
                {
                    
                    foreach (KeyValuePair<string, double> kvp in StartAirgroupAfterTime)
                    {
                        if (item.Name().Contains(kvp.Key))
                        {
                            Timeout(kvp.Value, () =>
                            {
                                item.Idle = false;
                            });
                        }
                    }
                });
        }

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

        SetAirgroupActivAfter(new Dictionary<string, double>
                            {
                                {"BoB_RAF_F_64Sqn_Early", 120.0}, //2min
                                {"BoB_RAF_F_111Sqn_Early", 180.0}, //3min
                                {"BoB_LW_JG51_III", 900.0} //15min
                            });
    }
}

With SetAirgroupActivAfter you can activate the Airgroup.
You can also use (for example)
SetAirgroupActivAfter(new Dictionary<string, double>
{
{"BoB_RAF_F", 900.0} //15min
});

to set all RAF Fighter units active after (in this case) 15min.