Set Triggers on a Collection
Triggers allow you to automatically turn public sales on/off. For your overall Collection, you can choose the exact date and time fees will go on sale to the public. Remember that sales will turn off at the Collection payment deadline. You are always able to sell via your admin panel regardless if your Collection is on/off.
To set a Trigger for a Collection, navigate to Collections --> Standard. Then, next to the desired Collection name, click Options --> Triggers.
To turn on the Trigger, click the toggle so that the bar is green and the circle is on the right-hand side. You will then have boxes where you can insert the date and time at which you'd like this Collection to be live for public sales.
Click Save Trigger to complete the setup.

Be sure that your timezone is accurate to ensure proper timing. To change the default option on your account, check out this article. Suggested Article: Change your account Timezone