public class AppodealInterval : MonoBehaviour, IVideoAdListener
{
    private static float _timer = 0;

    void Start ()
    {
        Appodeal.initialize("8b272aa477b3fb3a8ba0f2e1657e51efc");
        Appodeal.setVideoCallbacks(this);
        Appodeal.isLoaded(Appodeal.VIDEO);
        Appodeal.show(Appodeal.VIDEO);

        var deltaTime = Time.realtimeSinceStartup - _timer;

        if (deltaTime > 60 && Appodeal.isLoaded(Appodeal.VIDEO))
        {
            _timer = Time.realtimeSinceStartup;
            Appodeal.show(Appodeal.VIDEO);
        }
    }
}