When would be a good time to learn 3BLD?
The best time to learn 3BLD is whenever you have a cube handy and you have an hour or two of uninterrupted time to watch a couple of YouTube tutorials. You'll want to go slowly through the tutorials, pausing and rewinding often to make sure you're following the concepts. You'll want to choose a time after which you'll have a bit of spare time (at least 15 - 30 minutes) each day for a week or two to practice and revise concepts. You'll need this time to practice tracing your memo, getting used to labeling the pieces and knowing instantly where they go, and solving with your eyes open to make sure you understand how to apply the method, and how to deal with cycle breaks, etc. When you're ready to try your first blindfolded solve, choose a time when you'll have sufficient uninterrupted time when background noise will be as quiet as possible. I picked late evening after everyone else had gone to bed.
Interestingly enough, knowing how to solve a cube sighted is actually not essential for learning to solve it blindfolded (you just have to learn 3 algorithms) so your experience with sighted solving isn't that important.