Populate select field with time interval in Advanced Custom Fields

Question

I have an option page with 2 fields.

A number field for the time interval:
booking_settings_openings_hours_interval

And a repeater field with 2 subfields:
booking_settings_opening_hours_start
booking_settings_opening_hours_end

The code below creates a list of all times (with interval X) from START to END time to populate a select field. The interval code works great but it doesn’t populate the select field with these time options.

But when I replace:

// explode the value so that each line is a new array piece
$choices = explode("\n", $choices);

With this:

// explode the value so that each line is a new array piece
echo explode("\n", $choices);

it does populate the select field but that’s not the way how to do it right..?

function yl_load_booking_time_field_choices( $field ) {

    // reset choices
    $field['choices'] = array();

    $minutes = get_field('booking_settings_openings_hours_interval', 'booking_settings');

    // get the value from options page without any formatting
    if( have_rows('booking_settings_opening_hours', 'booking_settings') ) :
        while ( have_rows('booking_settings_opening_hours', 'booking_settings') ) : the_row();

            $start      = get_sub_field('booking_settings_opening_hours_start', 'booking_settings');
            $end        = get_sub_field('booking_settings_opening_hours_end', 'booking_settings');

            $startDate  = DateTime::createFromFormat('H:i', $start);
            $endDate    = DateTime::createFromFormat('H:i', $end);
            $interval   = new DateInterval('PT'.$minutes.'M');
            $dateRange  = new DatePeriod($startDate, $interval, $endDate);

            $choices = array();

            foreach ($dateRange as $date) {
                $dates = $date->format('H:i');
                $choices[] = $dates;
            }

            // explode the value so that each line is a new array piece
            $choices = explode("\n", $choices);

            // remove any unwanted white space
            $choices = array_map('trim', $choices);

            // loop through array and add to field 'choices'
            if( is_array($choices) ) {
                foreach( $choices as $choice ) {
                    $field['choices'][ $choice ] = $choice;
                }
            }

        endwhile;
    endif;

    // return the field
    return $field;

}

add_filter('acf/load_field/name=booking_time', 'yl_load_booking_time_field_choices');