Hi Amy!
With a 5 Day Magic Your Way ticket, you can go to the parks on any 5 days before your ticket expires, which is 14 days from first use. So in your case, you could, for example, go to a park the 1st day, skip the next 2 days, and then go the last 4 days of your vacation.
By the way, you can always add options to any ticket within 14 days from first use. So once you get to Walt Disney World, you could add 2 more days to your ticket for very little money; you can see the current prices
here. You could also add the Park Hopper option, the Water Park Fun & More option, and / or the No Expiration option.
Have a magical vacation!