There's no issue with taking both at the same time.
Other than the Whey will process faster, and you may need to get up in the middle of the night to pee.
But there's honestly no need to be taking the Whey before Bed, if you are already taking the Casein.
The Casein is more than sufficient to feed your body during your sleep.................... JP
P.S.
I would look for Micellar Casein as apposed to Calcium Caseinate.
The Micellar Casein is a little more expensive, but worth the money.