[enturn]

I'm fairly sure if you have the app on your phone you can download the map data and use it offline unless it changed (It's been a while since I've done it).

[int_19h]

They expire in about a month, and then the app will refuse to let you use that data. You should treat it as a cache, not as an offline map.

If you want true offline map, you'd need to use Bing, HERE or OSM.