Use iptables rules in the router to allow/disallow traffic at some hours of day, see this. You can totally block the traffic, or QoS it to oblivion on hot hours and increase it traffic later (join the iptables rules by hours to set the classid and then apply different QoS to then)
Finally, a caching transparent proxy might help, specially if everyone uses the same sites... it helps the normal browsing (by caching images, css, js, etc) and the updates (local copy if already downloaded). You just need a old computer with some HD and you are done.
For harder to filter services, you can usually block DNS for then... but if you allow it for some time, it might be cached by the clients on peak hours and still work.
Of course, if you control the clients, you can also configure most of then to only download off hours
Finally, you can be a BOFH, permit only allowed traffic and block the rest... or redirect it to some backdoor installer and enjoy the chaos generated