First, you'll schedule the Test campaigns to launch at your desired date/time by clicking "Launch" button.
Then setting the start date in the future to schedule it to launch at that time.
Second, you'll edit the current campaigns to end right before the new ones go live (i.e. at 11:59 PM the day before your new one would start at 12:00 AM). This is done by editing the Rules and specifically the Campaign Expiration field.
Finally, while the new campaigns are set to Live and the old campaigns are set to Disabled, you can go into the old campaigns and schedule them to re-launch in the same way you scheduled the new campaigns.