By switching time, I assume you mean the time it takes to try the second trunk if the first one is out of service. If so the two settings you need to tweak are "Retry Count for SIP Invite" which defaults to 6. I set this to two. And "SIP Trying Timer", this defaults to 500ms which may be OK, but you can reduce this if you have little latency between CUCM and the gateways.
Something to be aware of is how these interact. CUCM sends an Invite, if it does not get a "Trying" within the given time it sends another Invite but this time it waits twice as long. So the default is absurdly long - 6 retries means seven in total with delays of 500ms+1 second+2 seconds+4 seconds+8 seconds+16 seconds before it moves on to the next gateway.
You can also enable Options Ping on the trunks, then if the gateway is down the trunk goes out of service and calls will hunt on straightaway.
