If I had to choose between 30 seconds heads up time and 20 minutes, on a big buck, I'll take the 30 seconds.
I want enough time to get positioned and not feel I need to rush the draw. That's all I need. So, I guess a medium amount of time (not a voting option) is ideal.
I don't want a lot of time. Once, I had a huge 8 point loiter right out of range for 20 minutes or so. I couldn't calm my heart rate and my blood pressure spiked to the point that I could not focus my eyes. I shouldn't have shot but did and missed clean. This was 5 years ago and then and now I don't have high blood pressure or any issues and this is the only time in my life that has happened.
I'm guessing it was blood pressure or heart rate, really. All I know is that my heart pounded like I was sprinting for 20 minutes, and then eyes got fuzzy. Maybe I needed more cardio at the gym. As soon as the deer left, eyes were fine.