If time for today is less then 15:00 then all time slot will be avialbel for tomorrow, if it goes above 15:00 then only time slot with end time above 12:00 will be avialable for pickup

next-day-time-slot-adjusted-for-preparation-time.php

<?php

class pisol_axd659_next_day_cutoff{
	function __construct($cutoff_time, $next_day_time){
		$this->cutoff_time = $cutoff_time;
		$this->next_day_time = $next_day_time;
		add_filter('pisol_dtt_time_slot_filter', array($this, 'next_day_filter'),10, 2);
	}

	function next_day_filter($times, $date){
		
		$type = pi_dtt_delivery_type::getType();

		if($type === 'pickup'){
			$current_date = current_time('Y/m/d');
			$next_date = date('Y/m/d',strtotime($current_date.' + 1 days'));
			if($date == $next_date && $this->nextDayCutoffReached()){
				foreach($times as $key => $time){
					$end_time_of_time_slot  = $this->pisolTimeForCompare($time['id']);
					$end_time_of_time_slot_timestamp = strtotime($end_time_of_time_slot);
					$next_day_time_timestamp = strtotime($this->next_day_time);
					if($next_day_time_timestamp >= $end_time_of_time_slot_timestamp){
						unset($times[$key]);
					}
				}
				return array_values($times);
			}
		}
		return $times;
	}

	function nextDayCutoffReached(){
        $current_time = current_time("H:i");
		$current_timestamp = strtotime($current_time);
		$cutoff_timestamp = strtotime($this->cutoff_time);

        if($current_timestamp >= $cutoff_timestamp){
            return true;
        }
        return false;
	}
	
	function pisolTimeForCompare($time){
		if(strpos($time, '-') !== false){
			$times_array = explode("-",$time);
			return isset($times_array[1]) ? trim($times_array[1]) : $times_array[0];
		}else{
			return trim($time);
		}
		return null;
	}
}

new pisol_axd659_next_day_cutoff('15:00', '12:00');