Initially I thought with the way you described how you were doing this it was an issue of you waiting until the device appeared to be open before asking the question. In this scenario you say "Ok Google"... wait for the screen to light and the assistant to appear, then ask your question. I was going to recommend that you try this scenario instead, say "Ok Google, then proceed to ask your question without pause or hesitation." However when I tried it both ways I had no issues with the screen timing out on either attempt. In fact it stayed on for what seemed a very long time after it had answered my question... So then I thought perhaps it was a screen timeout issue. I turned my screen timeout down to 15 sec., the lowest it can go, and replayed both scenarios and again no issue. Are you asking really long questions? Stammering or stumbling while you speak? I can not reproduce your experience, perhaps there is some detail you can think of that you are leaving out.