Couldn’t agree more, but I admin that this breaks the narrative and sense of urgency of some ESs.
I too have this problem because I can’t remember the last time I played a full ES in one sitting. 
But, with old stories at least, the part where you can’t leave is clearly marked and it usually takes less than 40 AP. Enough to approximate the time you need, but it doesn’t enable you to play 1/2 and return later.
This comes from someone with a huge backlog.