Fed-Ex and UPS are usually pretty accurate about their delivery times. That is assuming it actually goes out on the right day. Sometimes you'll get a seller that prints the label on the day of the sale, which leads the shipper to believe it would be picked up that day, and then it isn't actually ready. This is the fault of the seller, not the shipper. But once it's actually en route, 95% of the time it will arrive the day they say it will. And that's if it's going ground. If it's next day air or 2nd day air, bump that up to 99%. In the case of air, they are contractually bound to get it there on the right day or risk losing the shipping fees.
USPS OTOH can be a crap shoot. Never ship anything time sensitive through the postal service. I ordered a CD through Amazon last year and they shipped it USPS. Took over a month. I actually got them to refund it, thinking it was lost. Then it showed up a couple days later, after I'd already bought another one. Now I have 2 copies of it.