Now understand that during this time your main site operation may be alittle off because the cron is not running every minute. Also this has not been tested so i am not sure if it will work. Also your talking about 45+ hours of sending email. Im sure your host also has a mail limit per day so you might want to check that as well.
Other than that all i can think of is that you will need to use a third party service to send that volume of mail.
It is basically the whole guts and glory of the server config settings.
If you do not have a VPS or a Ded server then you will need to follow the rules of your host or use a third party client to send that many emails.
You can try to integrate it with phplist which is a open source maillist but since you are not a coder you would not be able to do that very easily.
Also understand that sending that many emails it only takes very few people to mark your emails as spam to get you blacklisted. So make sure you are only sending email to the people that have selected to receive a newsletter from you in the privacy section. The mass mailing by default i believe removes anyone that has not chosen to receive the newsletter but you need to confirm that with ross here.
Why exactly do you want to decrease your mail limit from 250 to 200?