There are various methods to do this:
1) Create a browser bookmark
2) Create a shortcut
3) Drag and drop the browser URL to the desktop
Exactly how you do this depends on your browser and operating system, but below are some examples.
Your bookmark will be for the /signin page. Subsequently, after you have signed in again, the app will detect that you were previously signed in and will redirect to the map and restore your last used date and location automatically (unless you're using private browsing windows or similar).
Create a browser bookmark
Create a shortcut
Again, in Chrome:
Alternatively, you can click in the browser address bar and drag and drop the current URL (address) to the desktop: