There is no release date just somewhere in 2022. The whole thing is about testing and updating new functions like Nanite and Lumen.
UE5 is such a change from UE4 it still needs lots of work.
If you need an official version then it’s 4.26,
UPDATE We have all learnt the documentation has been updated as are the 4.27 Learning examples Subway Sequencer and ArchViz Interior DO SUCCESFULLY convert from 4.27 to UE5.0 despite what the documentation saying there is a problem
See Obsolete UE4 tools code and workflows - Development Discussion
I suppose when Epic Marketplace allows UE5 content we will know the answer.
You must make a backup as there is no way back to UE4.
I have written a post on how to use UE 5.0 latest source to test your code.
Visual Studio 2022 RC 2 builds and runs UE5.0 - Development Discussion / Unreal Engine 5 Early Access - Unreal Engine Forums
This will get you up to speed on UE5 really fast, but the PC minimum spec is quite high. I use a 64GB pagefile as it is cheaper than more buying more memory
Just depends on how long and how much time you want to spend