i tired it like it is described in this article on gidhub https://github.com/espressif/arduino-esp32/issues/1077
i stoped wifi and bluetooth on the first core of the ESP with the commands in the loop().
if(((now.hour() == 22) && (now.minute() == 0) && (now.second() == 0)))
but after the lines below there is only a connection for about one second than its disconnected again.
the wifi connection is executed from the second core.
WiFi.config(local_ip, gateway_ip, subnet_mask, dns_ip);
while (WiFi.status() != WL_CONNECTED)
if it is desired, i could post the full code, but maybe anyone had the same problem like me.