When should I add my customers to Starloop?

Generally speaking, it's best to add your customers into Starloop after they have transacted with you. 

How soon after?

Usually, ASAP is best. 

There are some cases where you might want to wait, such as if there are delivery times in play.  But for the most part, people will feel more likely to write a review while the experience with your business is fresh in their hearts and mind.