scratch_16.php

<?php
public function getDates()
{
    // In case it returns array of arrays:
    return [
        // You can specify second "element" which would be the name of the column with timezone values
        ['start_date', 'timezone'],
        // Use default if second "argument" not provided
        ['some_other_date_field']
    ];
}

public function getDates()
{
    // In case of returning array of strings - do what's Eloquent does right now.
    return [
        'column1', 'column2'
    ];
}