How about this:
2: In my Father's house are many mansions: if it were not so, I would have told you. I go to prepare a place for you.
3: And if I go and prepare a place for you, I will come again, and receive you unto myself; that where I am, there ye may be also.
John 14:2-3
Jesus said before we will be with him where he is he will have to come again and receive us to himself. I take this to mean at his second coming.
Instant Heaven doctrine says as soon as you die you are with him where he is.
Who should we believe?