The best alternative to 5300 is 5350 🙂 you will not find a better gateway in the market, I have worked all available gateways, Quintums are robust, Voicemasters are good in applications and functionality, but Cisco’s are the best of the breed.
The ability to cut a call after 30 minutes automatically has to be commanded externally, usually you use a gateway in combination with a billing or administrative platform that manages this parameters based on radius authentication and accounting, for example Voicemaster 2000 from Sysmaster, this equipment tells the gateway thru radius that the maximum connection time for a call is 30 minutes or whatever the amount of minutes that you set-up and the gateway will automatically cut the call at the pre-set time.
If you need more information post more details about your application and we may be able to help you.