Time to download SBCL from its website - 30 seconds. Not the problem.
Time to acquire the domain knowledge by learning about the different implementations and their respective strengths and weaknesses and decide on one (which could get nasty if you pick the wrong choice) - minutes to hours. That is the problem.
Time to acquire the domain knowledge by learning about the different implementations and their respective strengths and weaknesses and decide on one (which could get nasty if you pick the wrong choice) - minutes to hours. That is the problem.