I think it’s pretty rare that you understand a lab more when you take more time to do it.
It’s all about percent yield and purity, man. Well, sometimes. But it’s good practice, I suppose. I agree that spending more time in the lab won’t help, though. As my orgo professor says,
"A month in the library saves you weeks in the lab."
(i.e. if you’re adequately prepared then labs will be shorter for you)