Business days are Monday - Friday. If you order something on Friday that takes 3 - 5 business days you won't get it until at least Wednesday because the weekend days don't count. It also depends on what time you placed your order. Most places have a cut-off time for shipping the day the item was ordered. Usually it's around 3 pm. If ordered before that time it will ship that day so that's one day down. If ordered after the cut-off time, it won't be shipped until the next business day. Same with priority shipping. While it takes 2 business days, if you order it on Friday before the cut-off time it will arrive on Monday. If after the cut-off time, it will arrive on Tuesday. Of course all that depends on weather conditions, too. If there's a crippling snow storm, for example, than the delay could be several extra days. Hope that helps.
I've ordered a lot of stuff online.