Understand the fact that fees are not constant because of what we refer to as average congestions. The average fees fluctuate as more people broadcast transactions and use higher fees plus the higher the density of transactions on the network the higher the depth your transaction is placed. So the position of your transaction also determine how fast it'll get confirmed.

Also take note that your number of UTXOs required to pay for your transaction also contributes to how much you will pay in fees because of the fee rate and space the transaction will occupy in that block.