There are couple of features missing in Vaadin 24 DateTimePicker. 1: There is no automatic setting of time mode, which would be useful in some cases, 2: The time picker does not autoscroll to selected time if such exists. This Gist demonstrates JavaScript workarounds for these missing features.

DateTimePickerView.java

package com.example.application.views;

import java.time.Duration;
import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;

import com.vaadin.flow.component.datetimepicker.DateTimePicker;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;
import com.vaadin.flow.router.Route;

@Route(value = "date-time-view", layout = MainLayout.class)
public class DateTimePickerView extends VerticalLayout {
    private boolean hack2set;
    private DateTimePicker dateTimePicker1;
    private DateTimePicker dateTimePicker2;

    public DateTimePickerView() {
        dateTimePicker1 = new DateTimePicker();
        dateTimePicker1.setLabel("Automatically set time");
        dateTimePicker1.getElement().executeJs("""
                this.__datePicker.addEventListener('change', (e) => {
                    this.__timePicker.value='12:00';
                });
                        """);
        add(dateTimePicker1);

        dateTimePicker2 = new DateTimePicker();
        dateTimePicker2.setLabel("Scroll time to view");
        dateTimePicker2.setVisible(true);
        dateTimePicker2.setValue(
                LocalDateTime.now().plusHours(8).truncatedTo(ChronoUnit.HOURS));
        dateTimePicker2.setStep(Duration.ofMinutes(15));
        dateTimePicker2.getElement().executeJs(
                """
                        const timePicker = $0.__timePicker;
                        const comboBox = timePicker.$.comboBox;
                        timePicker.addEventListener("opened-changed", (e) => {
                            const scroller = comboBox._scroller;
                            if (scroller) {
                                scroller.scrollIntoView(scroller.items.indexOf(scroller.selectedItem));
                            }
                        });
                                                """,
                dateTimePicker2.getElement());
        add(dateTimePicker2);
    }
}