The longevity of the processing of the beatmaps depends on your amount of beatmaps, if you have a lot it will take a awhile. Though if it is getting stuck on a beatmap then it may never process. Lets try what is below.
Switch to cuttingedge release stream. Start up the game and when you go to song select open the osu! folder.
Let the maps process for a bit and when it eventually doesn't process them all copy and paste the contents of the runtime.log into here to see if it is getting stuck on a beatmap or something of the like.
To locate the runtime.log, this log file is found in the "Logs" folder inside your osu! folder.