Re: 1969-06-20 (Orbit Yuri Gagarin) - 1961-04-12 (first moonlanding) is slightly over 8 years.
Remember they chose to put big jointed solids (which cannot be shut down) on SLS after Challenger showed what happens if the joint fails.
At least they did two things right about that.
1. The crew compartment is at the top of the stack where the FSM intended it to be.
2. There actually is a Launch Escape System
(side note: Apollo 11 landed on 1969-07-20.