Laravel 5.5 whereDate/whereTime not add quotation

Appointment::whereDate('schedule_date', '=', date('Y-m-d')))->whereTime('time_from', ' <= ', date('H:i:s'))->whereTime('time_to', ' <= ',date('H:i:s', strtotime('+1 hour')))->get();

When this code is running on production server it responses nothing. Perhaps it is for quotation. But how to add this? I mean quotation(single/double).

via Chebli Mohamed