If you send a transaction it gets queued. There is a long queue of unconfirmed transactions. You can have a peak at them at
https://blockchain.info/pl/unconfirmed-transactions.
The queue is in fact arranged by fee (not by the send time(!) ), because it makes sense for the miners to include highest fee transactions first - the transaction fee goes to their pocket. There are exceptions (for instance you pay an accelerator explicitly to confirm THAT transaction, regardless of the fee), but otherwise it is a golden rule -
the queue is arranged by the fee, descending.
In bitcoin, blocks happen to be mined every ten minutes on average, but a block can contain only so many transactions - so the first transactions (as many as fit into a block) from a queue are included in a new block, the rest waits next ten minutes (on average) for the next block. But, if new transactions come, they may be placed first in the queue if they have higher fees. So your transaction may get pushed down and down the queue. Sometimes you have to wait
very long for the confirmation. My record waiting time is 2+ weeks, in Dec'17.
There are calculators that help you figure out the best fee - i.e. the fee that gets your transactions confirmed fairly quickly, but not exceedingly high. Example:
https://btc.com/stats/unconfirmed-txCurrently, it is 2 satoshis per byte, it is extremely low. In Dec'17 it was hundreds times more.
Now, if you send your transaction with a fee, even if it is low, it always makes sense for miners to include it in a block
eventually. But if there is no fee whatsoever - there is absolutely no incentive.
I hoped that answered your question
