Description:
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DateTime::modify() with parametrem 'weekday' loses time value.

Also date() function.

Test script:
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<?php
$date = '2020-11-27 12:33:00';

echo date('Y-m-d H:i:s', strtotime($date.' +1 day')); 
// Correct: 2020-11-28 12:33:00
echo date('Y-m-d H:i:s', strtotime($date.' +1 Weekday'));
// Uncorrect, lost time: 2020-11-30 00:00:00

$date1 = new DateTime($date);
$date2 = new DateTime($date);

$date2->modify('+1 day');
echo $date2->format('Y-m-d H:i:s');
// Correct: 2020-11-28 12:33:00
$date1->modify('+1 weekday');
echo $date1->format('Y-m-d H:i:s');
// Uncorrect, lost time: 2020-11-30 00:00:00