Navjeevan is Super Crowded train, being only train to Gujarat From Chennai. Even Rajasthanis Ajmer and Marwar region Hijack that train.
And It will reach in Evening to Ahmedabad, you have to rely on Buses from Ahmedabad to Bhavnagar.
So its Best if you Take Chennai Mumbai Express till Mumbai and then Spend some time in Mumbai and Capture Bhavnagar Express.
Or You Can...
more... Catch Chennai Dadar SF and From Bandra you can get BDTS BVC Holiday Special, but that train is Weekly only.