The DNS doesn't request over HTTPS. The process is that a client tries to visit an HTTPS site, the Pi-hole sees that the domain is on a block list and responds with the IP address of the Pi-hole. The client then sends it's requests the the lighttpd server and in the case of HTTP, it will be given the blockpage. In the case of HTTPS, since we do not have the certificates of the site you are trying to visit, you just get nothing in return. This can cause delays with the client timing out waiting for the HTTPS response. In order to avoid the timeout you can use the firewall capabilities of IPTables to reject the connection and the client wont wait for a response as it is told that the site doesn't exist and is not available.