How long does an ACH transfer take?

Could you elaborate on the typical time frame for an ACH transfer to complete? Is it a quick and efficient process, or does it require some patience? Understanding the turnaround time is crucial for my financial planning, so I'm keen to get a clear picture of the expected delay. Are there any factors that could potentially slow down the transfer, such as bank holidays or weekends? Clarifying these details would greatly assist me in managing my funds effectively.