> Even before the James Webb Space Telescope was launched, for example, the first call-out for proposals drew 1,173 ideas that would require 24,500 hours of prime observing time. But only 6,000 hours were available.

Can someone explain this to me? I've Google'd and not gotten much. 6000 hours is like 250 days. I thought the Webb has a 10-20 life. So how does that work? How much of each "day" is prime time? and why?