If we have the part in stock, it is not past our shipping cut off (9:00am PST / 12:00pm EST), and it is not Friday, then by selecting one of the "UPS Next Day Air" shipping options in checkout you should receive your part tomorrow.We recommend that in this situation you email us at shipping@fire-parts.com to make sure that we do have enough of that item on hand, as well as check with us if it is too late to get your order out if it is slightly after 9:00am PST (12:00pm EST)If it is Friday morning or Thursday afternoon, then no, your package will not arrive on Saturday or Sunday no matter which shipping option you choose.The differences between the three "UPS Next Day Air" options are the time of day the package is likely to arrive. "Early AM" is likely to arrive early in the morning. The regular "Next Day Air" option is likely to arrive late morning, or early afternoon. The "Next Day Air Saver" option is only likely to arrive sometime that day.After the package is handed off to the postal service, we then have no control over it -- we take no responsibility for any delays in transit. These delays are rare, but can happen; they are more likely to occur when there are poor weather conditions or during the holiday season.