After you join the Ads program if you don’t set time slots, the default setting is for pre-roll and post-roll ads to be inserted at the beginning and end of each episode (before and after your audio content).
However, you may prefer other times. And, you may want to consider setting mid-roll slots for new and top episodes, as these slots are popular with advertisers and often bring a higher rate. To manually set/edit ad time slots, please go to the advertising page and click on the “Ad slots” menu. You will be able to set times for pre-roll, mid-roll, and post-roll ads on episodes individually or by batch.
Here is the Video Tutorial
Set Ad Time Slots to A Single Episode
Click on the pencil icon to set/edit the ad time slots specific to a single episode.
Batch Edit The Ad Time Slots
Check on the position you want to change and set the time slots. Uncheck the box if you don't want to change the position.
Edit Ad Time Slots When Publish New Episodes
You can also set the ad time slots up directly when you publish a new episode.
Batch Delete The Ad Time Slots
Check on the position you want to delete and leave the time slot as blank. Save your changes.