Apparently, no option seem to completely satisfy your criteria: trains require changing the train in the night, and buses depart in the morning and arrive on lunch time.
The timetable of Kamianets-Podilskyi train station shows that the only two trains are:
№ 770 Kamianets-Podilsky — Kyiv (departure time 00:55)
№ 118 Chernivtsi — Kyiv (departure ...
I didn't see any results after 9th Feb, which is 15 days from now, so I went digging into the site's terms and conditions, where I found this relevant bit:
184.108.40.206. The extreme date of operations is determined by server of bus terminal (bus station, transporter). Of course it is not less than 15 days from current date.
So it appears that you can only ...