as far as i know there is no AnimationCompleted for such an animation
but you could use Sleep(3000) and then do what ever you want
B4X:
imgSplash.SetAlphaAnimated(3000,1)
Sleep(3000)
'do here what you want or call sub like:
imgSplash_AnimationCompleted
Sub imgSplash_AnimationCompleted
Log("animation completed.")
End Sub