When I don't drink coffee, it might take several hours for my mind to hit peak alertness, performance levels, but it when I do finally hit my stride, it seems to last longer.

When I drink coffee, I hit peak alertness/performance in 10-15 minutes, but then I'm crashing by early afternoon, sometimes even before that.

So the window in which I'm most alert and highest performing seems to shift when I drink coffee, rather than widen, say, 7:00am-1:00pm with coffee, for a 6 hour windows, compared to 9:00am-6:00pm without it, for a 9 hour window, but it's not open until later in the day.