While '60101' is a valid date in 'Gis' format (06:01:01), parsing it with date_parse_from_format will result in an error.
<?php
var_export(date_parse_from_format('Gis', '60101'));
array (
'year' => false,
'month' => false,
'day' => false,
'hour' => 60,
'minute' => 10,
'second' => 0,
'fraction' => 0.0,
'warning_count' => 1,
'warnings' =>
array (
5 => 'The parsed time was invalid',
),
'error_count' => 1,
'errors' =>
array (
4 => 'A two digit second could not be found',
),
'is_localtime' => false,
)