Don't give that sort of estimate. How could you know? Instead ask for time for discovery and then have a discussion with another dev about the proposal. When y

Don't give that sort of estimate. How could you know? Instead ask for time for discovery and then have a discussion with another dev about the proposal. When you do go to your manager say something like "With a day's work I'll be setup and ready, and then I say we keep going until I fail to make it faster for two days in a row." Then you didn't fail, you just did what you could.