All kudos to Martinez for wanting to wait for Lukaku to make up his mind with the hope of signing him in 2 weeks or so. But lets look at it from another angle.
According to reports he's not ranked high in Chelsea and he wants to play. He knows about our interest in signing him and he knows he will play football here. If he is just letting time pass for 2 weeks before signing for us, I'd be questioning his interest in playing for us. It would feel like he went here as a last resort, just because noone else wanted him, not because he wanted to be here. While I would be very happy that he signed for us at that time, I would also wonder if he is the right man for us due to his reluctancy to sign up.
It's one thing if the negotiation for the fee between us and Chelsea draged out, or if the negotiation of his personal terms took a while. But if it's just a refusal to commit because he's waiting for something better...