I’d love to see this added too, I’d imagine that setting the exact number of seconds isn’t necessary for most use cases and it makes the input a little confusing. An option to toggle this off in ACF would be ideal.
It’s a bit of a hack, but I fixed this by adding some custom CSS to my admin page that simply sets a display:none on the seconds selector:
function remove_acf_time_picker_seconds() { ?>
<style>
.ui_tpicker_second,
.ui_tpicker_second::before {
display: none !important;
}
</style>
<?php }
add_action('admin_head', 'remove_acf_time_picker_seconds');