It should arrive in time via normal mail.
However, I would like to bring up a related part of your post. You mentioned you ordered the SunPass Mini. This is a sticker; you will need to attach it to the car's windshield for it to work, and it does not peel off well (in fact, it will likely be destroyed when you get it off). In addition if you are renting a car, you'll want to be sure to peel it all the way off before leaving a vehicle, so no one else can use your account.
If you are driving and attaching it permanently to your vehicle, then good for you! If this is for a rental car, just keep the above in mind. If you do need a SunPass for a rental car, you can likely trade an unused mini for the larger portable version at a SunPass service center or just pick up a portable one at any Publix/CVS drug store.
Good luck!