I find that the only times I've missed the 8-12 hour window were when my starter was made too hot or too cold.
I make a typical 1L water/50g DME/0.25 tsp nutrient starter. Boil for 10 minutes, then cool. Pour into a 1 gal glass container, pitch yeast, shake the crap out of it. Loosen lid and start counting to 8 hours.
Normally, I just do this first thing in the morning on brew day. I got a pressure cooker not too long ago though, so I hope to start canning my starters.