The wait setting is the time between each email being sent.
"Send a maximum Of" is the maximum number of email to send in the time period specified in the Emails every Seconds setting.
it is best to set the wait time to match the maximum emails every number of seconds
so for example
Maximum Emails: 10 every 20 seconds
you would want to set the wait to 2 seconds.
UE Will try to over ride any server timeout settings so that the script wont time out, if the script is timing, then the server is not allowing UE to over ride the server setting, this will need to be corrected on the server.