Using recipe DME for yeast starter

Instead of using separate stock of light DME for a yeast starter, is there anything wrong or inadvisable about using the DME included in the beer kit/recipe? I am figuring that yes you're taking out (let's say) a cup of DME from the recipe to use for the starter, but you're then adding it back in if you pitch the entire starter. Thoughts?

Secondly, this is my first time making a starter. I also have a stir plate. When should I be pitching the starter? Is 12 to 18 hours on the stir plate about right?

Thanks!

Other than taking away from the finished beer, you can use the DME from the kit. I usually try to pitch an active starter between 12-18 hours. If I can't hit that window, then I'll stick it in the fridge. Pitching the whole starter isn't too bad for small starters, once you start making 1L starters and over, you may want to cold crash the starter, decant off most of the starter beer and pitch the remaining slurry. A starter can get nasty pretty quick if left out too long. good Luck!

So it's good to use the DME from my recipe for the starter then? Or is it better practice to use separate DME?

I am torn between pitching the entire starter or just the slurry. I've read that cold crashing and pitching just the slurry can be beneficial, but because you're cold crashing you're putting the yeast back to sleep rather than when pitching the entire, active starter.

I am confused and can't decide what to do!

I would recommend using DME not from the recipe to make your starter. Yes, it was going into the recipe anyways, but you're also adding extra water when you make the starter. Unless you account for that when you fill your fermenter, you'll be slightly cutting your gravity by adding the starter.

As for pitching, I've had plenty of success pitching a 1 liter starter in it's entirety. Give it about 12-18 hours of a head start, pitch to the wort and you'll have healthy, active fermentation very soon.

Just my 2 cents