we are thinking to implement Shipping Integration (Fedex and Netsuite). If I understand well, it will automatically connect to Fedex / Netsuite, get the tracking number and print the labels. For us, it's slightly different. Would it be possible to get the tracking, the label and later, about an hour, print the labels ? Also if I'm not mistaken, the info is saved on the Item Fulfillment ?

You need to check the Shipping Label Integration box on the Item Fulfillment so that you can automatically generate the tracking numbers and manually print the shipping labels (assuming you are using integrated shipping items). You can print the shipping label at a later time since it is manually triggered anyway. But as mentioned, you can print it only when the Shipping Label Integration box is checked on the IF. Yes, the tracking numbers are saved on the IF.