Is this normal?

At 39 weeks exactly (three days ago) I got checked and was 3cm, 80% effaced and baby’s head was super low (zero station). Doc said he wouldn’t be surprised if I went into labor that night or at least within 48 hours. Cut to this morning and nothing is happening! Is this typical? With the head so low he said it would go really quick once it happened. Why hasn’t anything happened yet? Is it normal to be this dilated, effaced and low and still not go into labor??