In your Inventory>Activities, click to add an activity and then select the option of Time slots.
You can click on the edit icon under Time slots to add the times for this activity.
You can choose the time slots according to your preference:
In the pricing section, use the quantity column to set up different prices according to your preference. Note that each time slot selected in the frontoffice will be counted as a quantity of one.
Here is how this activity will be presented in the frontoffice:
If you want to offer multiple "scheduled activities" in a package, please refer to this article.