ok i think u right it is uncovered
but when i read this question something came to my mind
which is
make an ACL (time based ACL) that permit lets say h323 signaling in a spicific time to one gateway and to the othergate way in other time
and make two dial-peers with same config and each one point to different gateway based on ur above requerment
and make prefrence for one of them 1 and the other 2
so think when the ACL blocking call signalling for one gateway in a particular time the dial-peer will try to hunt and go to the other dial-peer with the same destination
which should be allowed by the ACL at that time
(u may want to route ur calls during working hours to gateway1 and after that to gateway 2
just make ACL time based block callsignalling for gateway one during working houres and
make two dial-peer to the same destniation
one for gateway one with prefrence 1
and the other for gateway2 with prefrence more than one ( 2, 3 .. )
and try to decreas the h323 default time when move between dial-peer by default 15 second
so u have to wait 15 second to go to dial-peer with higher prefrence number by defaul)
try it and let me know
Rate if helpful
good luck