Downloading offline maps and all associated data is fairly quick (depending, of course, on the size of the country and the speed of your internet connection), but setting it up correctly on your device can take a long time. Downloading and setting up are all part of the download process in your app. The download time can take anywhere between 2 and 20 minutes on average. It takes a while, but then you have everything you need for your journey!
In the meantime, you can continue searching for locations or (if you have Android) use another app on your device. The download will continue as normal.