The moment you place your order is the moment that decides. If a giveaway is open at that moment, your order earns entries into it. If none is open, the order earns nothing.
Placing the order is what counts, not paying
This matters near a deadline. The clock we check is when the order was placed, not when the payment finished clearing, and not when the order ships. So if you place an order before entries close and the payment settles a few minutes later, the order still counts toward that giveaway.
Entries are then recorded once the payment clears, which is why they can take a moment to appear in your account. That is a display delay, not a scoring one.
If no giveaway is open when you order
The order earns no entries at all.
Entries do not bank, and they do not roll into the next giveaway. There is no waiting room. If you want an order to count toward a giveaway, place it while that giveaway is open.
This is worth knowing if you are shopping in the gap between one giveaway closing and the next launching. The store stays open in that gap and you can buy anything you like, but the order will not carry entries.
How to tell whether one is open
The store shows the giveaway that is currently running. Your account at account.shftdco.com shows it too, with a live countdown while it is open. If My Entries shows no active giveaway, none is running.
If more than one giveaway is open
Your order earns entries into every giveaway that is open at the moment you place it. One order, separate entries in each pool, worked out independently for each. You do not have to choose between them and you do not lose anything by having more than one running.
Each giveaway has its own pool and its own odds, so your odds in one say nothing about your odds in another.
Once the giveaway closes
Your entries stay exactly where they are. They are recorded permanently against that giveaway and they are never removed. When entries close, your giveaway moves out of the active section in your account and into Awaiting draw, then into Past giveaways once the winner is announced.
A later order cannot be added to a giveaway that has already closed.
Buying a Fast Track pass near a deadline
A pass follows the same rule as everything else. It earns entries into whichever giveaway is open when you place the order, and nothing if none is open. Buying a pass after entries close does not hold anything for the next giveaway.
Where to check
Sign in at account.shftdco.com and open My Entries from the account side navigation. Each order page in your account also shows what that specific order earned. If an order you expected to count is showing nothing, the free troubleshooting steps are in the article on entries not showing.