The application was created before AutoCAD 2020 existed. If you have a previous version of AutoCAD like AutoCAD 2018 you can install it on that machine, be sure to run that version of AutoCAD before attempting to install the download. Then you can simply copy the files in the directory that gets created. In AutoCAD you would want to set your PREFERENCES to include that directory as a SUPPORT directory and also a TRUSTED directory. Then you should be able to use the launcher or use the AutoCAD command NETLOAD. The launcher will use the last version of AutoCAD that was active. NETLOAD will then prompt you to select a .DLL. You would browse to the ArcGISforAutoCAD.dll when using netload. The next release available this summer will include an installer for AutoCAD 2020.
This is a valid workaround for using it with AutoCAD 2020. The hardest part is just getting the installer to run. If you have a version pre 2020 the installer should work just fine and then you can open AutoCAD 2020 and netload the plugin.
If you need to deploy it across machines that only have 2020, you will first need to download it to a machine that has a pre 2020 AutoCAD, copy the installed files and place them on the 2020 machines. You will then be able to netload the plugin using the ArcGISForAutoCAD.dll.
I can't give an exact date as its a bit of a moving target right now. The team is working on finishing some stuff up with the release. But I would say that it should be within the next several weeks assuming all goes to plan. You can currently get the software Release candidate for 400 if you sign up for the ArcGIS for AutoCAD beta site here https://earlyadopter.esri.com/key/ArcGISforAutoCAD