Once you've registered and paid for it you can update it weekly when the site is updated. From what the website says, it looks like there is no set time limit for updates. I copied this from the website.
Then come back as often as you like and download any additional specialty guides (usually available at no additional charge) and updated versions of the first edition of Walt Disney World To Go in any or several of the available forms. One registration fee covers all versions used (iSilo and Plucker or Online) on any one device or per family.