Inherited System - Changing the evening alarm setting

I inherited the digital life security system in the home that I purchased and I do not have an active account, but have been using it in a localized setting. However, the system keeps adjusting the time at which the evening alarm is set. When I first moved in, it was at about 10pm and the setting time has drifted to 9:20pm. Is there a way to change this setting without reinitiating service?

Thanks!