How long does ERC20 transfer take?

Could you please elaborate on the duration of ERC20 transfers? I'm particularly interested in understanding the factors that might affect the speed of these transactions. For instance, does the congestion on the Ethereum network play a significant role? Or does the size of the transfer have any bearing on the time it takes? Additionally, are there any techniques or best practices that can help expedite the process? Your insights would be greatly appreciated as I'm seeking to make informed decisions when it comes to ERC20 transactions. Thank you in advance for your detailed explanation.