Balance between minimum transaction fee and time using Electrum 3 Yesterday I made my first Bitcoin transaction using Electrum and I was able to configure the fees I was going to pay. As it was a non-urgent transfer I selected the minimum fee Electrum allowed me: "Within 25 blocks", the lowest sat./byte available from the slide bar.



If the transaction was supposed to be included in the next 25 blocks, I thought it will take around 250 minutes (~4hours) to be processed. But I don't know why, after 2hours the transaction already had 6 confirmations.

This minimum fee ended up being 0.0008 BTC (~10 € as the time of writing, which was ~14% of the sent amount).


Why did the transaction went so fast if the fee was for 25 blocks?
As it was a non-urgent transaction, couldn't I have selected a smaller fee in any way? I couldn't find a way to pay smaller fee in Electrum 3 --I could have waited for 24h with no problem to avoid this high fee.
Does this means that I paid much more for the fee than I could have paid, given the non-urgent requisition of my transfer?
It's all about bitcoin, the Electrum wallet is just a wallet, it doesn't minning block nor building block.


  Why did the transaction went so fast if the fee was for 25 blocks?


You can't predict in which block exactly your transaction will be added. 
The block is filled with arbitrary transactions. *


 * While larger fees improve the chance to be included in the block there is still have a chance to be added to the next block.
 


  As it was a non-urgent transaction, couldn't I have selected a smaller
  fee in any way?


You can select any fees what you want(and 0 fees also), but there are no warranties what that transaction will be added to the block. Transactions that pay more fee take precedence. 


  I couldn't find a way to pay smaller fee in Electrum 3 --I could have
  waited for 24h with no problem to avoid this high fee.


You can set commision manually in the Electrum settings.




  Does this means that I paid much more for the fee than I could have
  paid, given the non-urgent requisition of my transfer?


Transactions (with a small or zero fee) which stay unconfirmed for a longer time usually don't get priorized over transactions with a high fee. 
Every miner is free to chose which transactions he is going to confirm in his mined block. Its all about how the node is coded to fill the block with TX's.
Since miners mine because they want to gain profit, they will always priorize transactions with a higher sat/B fee.

From me:


  What happens with transaction with zero or low fees?


Generally, after a few days, the transaction will be removed from the mempool and your wallet shows your balance again, which makes your coins 
spendable again via wallet.