A woman after my own heart...I like to practice alone. We are a rare breed it seems. I find that individual practice is absolutely necessary to my dancing!
I do about an hour to two hours whenever I can. My usual routine begins with "laps" of rumba walks (with and without arms), then rumba walks with spirals, then I start mixing in whatever turning combinations I am currently working with. Next I do the other 6 rumba walks...with special emphasis on forward walks turning (my nemesis). Then I like to do the whole thing over again in Cha. For Samba I do stationary samba walks, progressive samba walks, L/R voltas, F/B boto fogos, and whisks. If I am having a tough spot in a Samba routine, then I run that through too. Paso I work walks and cape positions. Jive I just have some fun individual amalgamations I do for foot speed. Other "stuff" I throw in where and when necessary. You can never do these basics enough, always improving centering, balance control, turning, spotting, foot position, and a myriad of other things

After doing this for awhile, I can run through this bit in abut an hour. However...I started out SLOW many years ago! There is nothing worse than practicing the wrong thing!!! Show your coach every exercise and make sure that you understand it inside and out before you go off on your own. Get the ISTD technique books to check specific points.
Good luck, M