Laravel Pivot table extra date-time field format (Not timestamp) using carbon object

The best solution I would suggest is creating custom pivot model for this relation:

// Offer model (the same goes for the User model, but change to 'instanceof Offer`
public function newPivot(Eloquent $parent, array $attributes, $table, $exists)
{
    if ($parent instanceof User) return new OfferUserPivot($parent, $attributes, $table, $exists);

    return parent::newPivot($parent, $attributes, $table, $exists);
}

// OfferUserPivot
use Illuminate\Database\Eloquent\Relations\Pivot;

class OfferUserPivot extends Pivot {
   // override either property:
   protected $dates = ['use_time'];

   // or method:
   // public function getDates()
   // {
   //   return ['use_time']; // and other columns like created_at etc if you like
   // }
}

// Then you can do this:
$user->offers->first()->pivot->useTime; // Carbon object
$offer->users->first()->pivot->useTime; // Carbon object