you have the time between email set to 1 second.
it will send an email a sec up to 20 emails then pause until 2 minutes is up, then send another 20, with a wait time of 1 second between each email.
to force the wait time between emails, you could change the settings to:
Emails Every: 2
Seconds Between Emails: 6
use 6 seconds between the email to send 20 every 2 minutes (120 / 20 = 6)