Create the promotion
Create a version
In the campaign’s version picker, click New version, then turn on Time limited promotion.

Set the dates
Choose a Timezone, then set the end date and the Last referee purchase date (the cut-off for friends to qualify). Leave Start promotion immediately ticked to begin the moment you launch, or untick it to schedule a start date.
Build the version
Edit the sections as usual. See the campaign editor.
You can also turn a standard version into a promotion at launch: the launch wizard’s Schedule step offers Time-limited promotion. A promotion cannot run an A/B test.
Launch it
Open the launch wizard
Click Launch, work through the steps, and choose Schedule launch for a future start, or launch now.