How to Add time picker

Contact Form 7 has some Datepicker support via the new HTML5 date input type (see https://contactform7.com/date-field/) but this is currently only supported on some browsers – see https://www.wufoo.com/html5/types/4-date.html

Contact Form 7 does provide jQuery UI-based fallback for the date and number input fields. See https://contactform7.com/faq/does-contact-form-7-support-html5-input-types/

You can now also use Contact Form 7 Controls to implement this without writing any code – use the “Enable HTML5 input type fallback” option.

I am looking for to add timepicker

This is not available directly in Contact Form 7. It can be done via custom programing but you would need to be rather skilled at WordPress development using PHP and/or jQuery.