I recently sorted through 20 years of negs to print a portfolio. Some negatives that I had bypassed or given up on made it to the final 12. Vision changes and so do materials and skills. What is the longest I have worked on a negative to get it right? Probably a couple of days, but don't force it. Average is 2-3 hours, but it had better be worth it. If it doesn't excite you, you'll never get it. Put it down and print something that excites you. It that doesn't exist, try rephotographing a place that excited you, but the negatives just weren't that good.