In the past I have used two separate CF7 tags for this purpose - a Date tag where the website visitor enters the date and separate Select tag where the visitor selects from a dropdown list of times as follows:
[select prefertime include_blank "07.00" "08.00" "09.00" "10.00" "11.00" "12.00" "13.00" "14.00" "15.00" "16.00" "17.00" "18.00"]