That's dependent on how many transacitons, how many nodes, and the amount 1BTC is worth.

If the fee is uber low, there are many transactions, not as many nodes, and 1BTC is with 1USD, then the likelyhood of a timely transaction is low.

The less demand (transactions) and more supply (nodes), the more likely it will be processed. However due to the low fee (priority) it will be processed at a later time depending on the other two factors as well



If it does work that way I think once there are enough nodes/transactions, priority should be affected by the time passed from the transaction as well. You could have a transaction with 0BTC fee occur yesterday, but it would have a higher priority than a transaction with a 1BTC fee made 5 minutes ago.