CiviMail: Sending your email
Sending the email
On the last page you can choose to either send immediately or to schedule it for a later time. Choose whichever is appropriate.
Note: A script must run to actually send the emails. You can call it manually be going to http://example.org/civicrm/mailing/queue&reset=1 where example.com is your domain. An automatic script (cron) can also be set up to run periodically.
Before sending, you will want to check with your web host to ensure they do not have limits set as to how many emails you can send an hour. You don't want your account to be suspended because you broke this rule.