Getting your one-time customers to buy a second time takes proper timing.
Send marketing messages too soon and you'll disengage customers.
Send them too late and you'll miss other customers who ordered elsewhere.
This is especially important if your products are consumable or otherwise refillable. If someone orders a 30 day supply, you can expect them to reorder 30 days later. Non-consumable products also have buying cycles but they are more difficult to detect.
To figure out when to start promoting to one-time customers, you'll want to calculate the Customer Purchase Latency. This is the average delay between the first and second orders.
You'll get a number, like 65 days. That means there's a 65 day delay between the first order and second order.
One warning: I hear about stores using the store-wide Average Latency for this which is wrong.
The Average Latency is for every purchase. The second, third, fourth, even 100th. Since repeat customers tend to order sooner and more frequently in later purchases, that Average Latency is too optimistic.
That's why you want to use the latency between the first and second orders when you're marketing to one-time customers. In Repeat Customer Insights that'll be in the Order Sequencing Analysis and 1-to-2 Customers focus.