I have cable service with Charter and we have several channels (which we are subscribed to) which will not show during the day but in the late evening they show perfect. Everyday its about 9:30 - 10:00am the channel goes out and is not available until later in the evening. This is very strange
Although I can't answer your specific problem I can tell you that even though cable lines and their connections are insulated with a shielded braiding things such as the sun can still affect your cable signal. This could be why your channels come in better at night than during the day. As an example something like a sun spot can cause a cable outage.
Intermittent cable channels on a digital system can be caused by either inadequate signal OR excessive signal. If you have a cable amplifier in the system try bypassing it. Digital cable boxes have a narrow window of signal strength that they are happy with. Your provider should send out a tech with the right equipment to measure this. On your own you can also try to reboot the box or get a box replacement to try.