Unless a campaign status is Stopped, Finished or Processing, you can amend its scheduled day and time.

For example, if your Weekly Listings currently goes out each Thursday at noon, but you would prefer it to send each Wednesday at 5pm, you can easily amend this to suit. 

To start, navigate to the Campaigns menu, and click on the campaign you wish to amend.
From here:

• If the status is Scheduled, click the Pause button. The Date & Time module will then become editable.
• Looking at the Date & Time module, adjust the day and/or time by clicking on the sections to reveal the relevant drop downs.
• Once you have made your changes, don't forget to click the Save & Activate button to re-start your campaign.

You can also amend other elements to the campaign, like the recipients or the email being sent.

If you are a user wishing to change the day and time of your campaign to something different to the rest of your office or group, check Changing a campaign that has been set up by your Admin.