Confusing directions for Message limit for queue processing

So the help message for Message limit for queue processing states:

“Set the maximum number of messages to be sent at a time during queue processing. By default, all messages will be processed.”

I understand all messages will be processed in one go at it when the queue is kicked off via a cron, however, if the queue kicks in again in x minutes and the total number of messages has not yet been reached are we still expected to understand that the processing from the first kick-off of the queue is still running and the second call from the queue is ignored?

And with the following help message “Time limit for queue processing” stating “Set the maximum number of seconds allowed to pass while processing the queue. If the set timelimit is reached, processing will continue with the next call. By default, no timelimit is set.”

So does it follow if I have crons for every 15 minutes and not all of the messages are processed in 15 minutes by setting the queue processing time limit to nothing the next cron job will kick it off? But if I set this value to 360 seconds or 6 minutes, then am I to understand that the queue will stop processing after 6 minutes and wait until the next cron job kicks in?

And finally, as in phplist, can a time delay be introduced into the sending of emails?

Thank you.