Registration Renewal on RTP300

I am using an RTP300 (PAP2 with router) and was trying to find the best setting for registration expiration. Using the screenshots here: http://support.voipo.com/screenshots/pap2t/ I configured most of the settings, but it shows 60 seconds for registration. It seems excessive to me, but it is working fine renewing every minute. Suggestions?

I usually go 900 seconds on my stuff.

I use 20 minutes (1200 seconds).