Woodland's blog indicates that you will still get cells reproducing for about 48 hours. So, if you cut things off after 24, you might not be getting the most out of your dme. This is new to me. I usually cut things off after 24, but I may start to extend things
If you have a refractometer check the gravity when you pull your yeast off the plate. The yeast have eaten the sugars after 18- 22 hours, anything after that you are just running them through a spin cycle.
I ended up leaving it on the stir plate for about 36 hours and then put it in the fridge for about 6 hours. I used my refractometer and the FG was 1.012. My target was 1.010 so not too bad. After I pulled it out of the fridge and it warmed up, I was able to decant off about 300 mL. I pitched the starter this afternoon. After only about 4 hours I have a nice krausen and the airlock is bubbling.
Next time, I think I will leave it in the fridge longer so I can decant more. After only 6 hours, the yeast hadn't 100% settled.
I like 18-24 hours in the fridge. I decant as soon as I pull from the fridge rather than allowing it to warm up first. One other thing I watch for while it is on the stir plate is bubbles. If you hold a flashlight on the side of flask and you can see the bubbles swirling and rising in the starter. If you look at it while it is actively fermenting you get an idea of the activity. If you check after 18-20 hours it will still show bubbles, but not too many. Also before placing on the plate I give the starter a vigorous shaking or injection of oxygen before pitching the yeast. So I think 18 hours on the plate, 18 hours in the fridge is better than 36 hours on the plate.
I pull it off when you stop being able to see CO2 bubbles and all foam has fallen. Shortly after, the internal temperature will drop 1C or more, and it shows on my stir plate probe. That's usually around the 24 hour mark.
Refractometer indicates over a 70% attunement every time, so I just call it good enough. I'd rather have a longer cold crash so I don't decant off the cells I just worked so hard to create.