I know, I know, wait is hardly the right term.
When I get a new spindle, it's either at a show or through mail order. The ones at shows are put to use immediately, with some fluff from the vendor during purchase and then something in my current-spinning bag right away.
For a mail order spindle, I wait about as long as it takes to get the box off the porch :-) if it doesn't have some fiber tucked into the spindle, then a stash-piece is put to good use for its right-out-of-the-box first spin around the block (um, house).
Usually I'm dreaming of projects when I order the spindle, so by the time it arrives, the fiber's already in a tote bag and waiting only for it to complete its test run (as described above...)
So, how long do you wait to spin a new spindle? Comment here or linkback in your blog.