it depends on the "situation"
you should trust Electrum to give you a good estimate. it has been good so far that i am using it. the "situation" is based on the number of unconfirmed translations in the mempool and the fee that others are paying (the competition). when the competition is fierce you need to pay higher amount and if you pay less your priority will be low so your transaction will take a long time to confirm.
for example 6 days ago i sent a transaction with 4 satoshi/B fee and it was instantly confirmed (a couple of seconds as 1 block was found immediately after i broadcast the tx).
but today mempool i full AKA there is competition so the same amount of fee will be low priority.
