You will know when the time comes. It's the hardest and bravest thing you do for your loyal loving friend. It's better a day early rather than a week too late. Keep talking with your vet and let yourself hear the advice. It's just a horrid time and I'm so very sorry for you. Jarvis will show you. You know each other so well.
We were very blessed in that we were able to plan for the vet to come to the house and we could be with him keeping him calm and secure and loved. I know I went to the vets a lot at the end trying to measure and decide.I was scared I d get it wrong and my boy would suffer. It was tough. We are on the other side now and I think we got it about right. It's a very fine balance.
Your post really touched me as I understand so clearly that wondering time when you're trying to work out the best way to handle things.
I'm sending you wishes for better news and strength to cope with each day.
