Seemed to have fixed it by using this. Maybe someone knows if this is the correct way? Maybe there’s a cleaner way?
$locs = get_posts(array(
'posts_per_page' => -1,
'post_type' => 'locations',
'orderby' => 'monday_start_time',
'order' => 'ASC',
'meta_query' => array(
array(
'key' => 'monday_start_time',
'value' => '',
'compare' => '!=',
),
)
));