Yes there is. By default, SAIL sets asterisk to listen for 6 seconds of silence to detect the end of a voicemail. This is to guard against possible "runaway" recordings if, for some reason, a hangup isn't detected. Also; mails of less than 8 seconds are discarded. You can change these settings to suit your own requirements in the voicemail tab in the headers section.
Kind Regards
Selintra