Don't worry
20hrs or so for me.
Your first solo is much like a good whiskey, the longer you leave it the better the experience!
I done mine on a cold (very cold -25C) morning in Canada... Everyone knows you are doing it even ATC seem excited for you. As far as my instructors they drowned me with freezing cold water on an already cold day!
However long it takes you will remeber it vividly for the rest of your life I'm sure!
Mike