How much time should be dedicated to Research before a launch?
This depends on the magnitude of the launch, the goal of the research, and the budget available. For a large business-critical launch, you may have more than one phase of research. You might do a phase 1 a year out from launch, validating the product's appeal in the intended market. You might need a phase of pricing research 4 to 6 months from the launch. And I also recommend a phase of message testing research 2 to 3 months from the launch.
We are yet to use "it depends". well, it depends.. on how much time you have for your launch, how much risk is associated with the launch and how big your budget is. I recommend breaking the research into two parts. Discovery and validation. former to understand trends, topics and issues. latter to ensure you are on the right path.
Before a new product launch, I would hope that you've already done all your research by then as launch should be all about the actual GTM motions. Things I like to test right before a launch is putting drafts of GTM assets in front of prospects for their reactions/feedback. For example, I had invested on creating a short promotional video for launch day. When it was nearing its final stages of production, I shared it with a small number of prospects to get their feedback. I believe that any major marketing assets should be tested with an external audience before launch day to make sure you're going to be captivating your audience as much as possible!