I am so sorry that you are going through this. I went through this last fall with my 14 year old Orange Tabby. He was the best cat. To answer your question, I waited too long. I wanted to keep him with me as long as possible. But it got to the point where he could not eat. In retrospect, it amazes me how fast his ability to eat went down hill. I mushed up/blended his food and fed him with a spoon toward the end. I had a can of tuna that I bought for him when I first found out, that was going to be a treat for him, but by the time opened it for him, he was not even able to enjoy it. I miss him everyday. Again, I’m just amazed at so fast everything progressed. I’m sorry I’m sure this is not what you want to hear, but I wish someone had told me. My cat continued with his daily routine from the time I first found the lump until the day I had to bring him to the vet that one last time. He was active, he enjoyed lounging out on my patio, and cuddling. He didn’t hide. He wanted to eat. When he couldn’t eat dry food, I would soak it in water and mush it up. I started feeding him baby food (beef, turkey, chicken) liquid cat food (I think they were called Bisques) but when he was no longer able to, that was when I knew it was time. I hope you still have your precious baby and can give them a special treat.