Yes, ListMessenger has the ability to send X number of messages, then wait X number of seconds before sending more messages. These settings can be set by logging into ListMessenger, Control Panel, Preferences, Program Preferences and changing "Messages Per Refresh" and "Pause Between Refreshes".
Please keep in mind that if you set "Pause Between Refreshes" too high it may result in PHP reaching it's maximum execution time and the sending program will just time out. Setting it to 10-15 seconds should not pose a problem and is more than enough time for a mail server to send 10-100 messages. The default setting is 1 second.