There is no time limit on accessing your tour once it's been purchased
Once you've purchased your tour, you own it and can download and listen to it as many times as you like, whenever you like. If you sign out of your account, when you sign back in, you'll find the tour available to download again in the Purchased or Library folder. You can also access the tour via the VoiceMap website or mobile website. Just make sure to sign in with the same account you used to purchase the tour.
You can also listen to the tour at home in the app by tapping the Virtual playback button. This disables GPS and plays the tracks one after the other, like a podcast.