As I mentioned before, I just used a starter AND stirplate for the first time last Monday. Mine stirred for just about 44 hours, from afternoon on Monday to mid morning Wednesday... pitched at 3pm Wednesday.
My guess is your yeast will have an obvious line where it separates from the wort and you can just slowly pour off the wort, leaving the yeast slurry behind.
Most will leave a little wort behind to have some liquid to stir the yeast up.. if not, you'll be pouring something like syrup down the flask into the fermenter.
Good luck Thursday, keep us posted if you can