Fade in GameObjects after a number of seconds. With nice curves.

FadeInAfterSeconds.cs

using UnityEngine;

/// <summary>
/// This component fades the component in after a number of seconds. For it
/// to work, it needs to have a MeshRenderer, and the MeshRenderer needs a
/// material that lets you set the alpha, otherwise it totes won't work.
/// </summary>
[RequireComponent(typeof(MeshRenderer))]
public class FadeInAfterSeconds : MonoBehaviour {

    /// <summary>
    /// Time after level load to begin the fade in, in seconds.
    /// </summary>
    public float delayTime = 1.0f;

    /// <summary>
    /// The amount of time to go from the begining of the fade to its end,
    /// in seconds.
    /// </summary>
    public float fadeInTime = 0.3f;

    /// <summary>
    /// The animation curve to follow, where the evaluated value is suppose
    /// to be the alpha of the mesh.
    /// </summary>
    public AnimationCurve fadeInCurve;

    /// <summary>
    /// The mesh renderer we need to adjust the alpha of. It's set when the
    /// component awakes.
    /// </summary>
    private MeshRenderer meshRenderer;

    void Awake() {

        // Grab the mesh renderer and cache it.
        meshRenderer = GetComponent<MeshRenderer>();
    }

    void Update() {

        // Work out how far we are into the fade so far.
        // NB: If the fade time is zero (or less), we use a super low
        // number to make it seem like it's fading instantly. It's a bit of
        // a hack, but it means no accidental divide-by-zero errors.
        float amountIntoFade = 0 - ((delayTime - Time.timeSinceLevelLoad) / (fadeInTime > 0f ? fadeInTime : 0.001f));
        float curvedValue = fadeInCurve.Evaluate(amountIntoFade);

        // Set the mesh renderer's color to its current color, but with the
        // alpha from the curve.
        meshRenderer.material.color = new Color(meshRenderer.material.color.r, meshRenderer.material.color.g, meshRenderer.material.color.b, curvedValue);

        // If we've completed this fade, we can disable the component,
        // since it won't be needed again.
        if (Time.timeSinceLevelLoad > (delayTime + fadeInTime)) {
            this.enabled = false;
        }
    }
}

Published under the Do What the Fuck You Want to Public License. Enjoy!