Since Starting This Flow vs Over All Time

Welcome to the community @Misaky 

The condition would be ‘since starting this flow’, however, you do not need to use conditional splits for your use case. 

Set a flow filter to ‘What someone has done (or not done)’ = placed order zero times since starting this flow’. That filter is evaluated before each email is sent. So a contact who has subscribed to your list will be skipped from an email if they have purchased while in the flow. This approach does assume you don’t have a delay before your first email otherwise it’s possible they subscribe then purchase and don’t receive email 1. For this type of flow where a discount is often offered, I don’t include an initial delay as that first email is their incentive to purchase.

Alternatively, if you want to keep your delay, you could just add the same condition ‘What someone has done (or not done)’ = placed order zero times since starting this flow’ to emails 2 and 3 as an additional filter (below). That will also skip contacts who have purchased.

Hope that helps

Andy