Congratulations on coming back from such a bad accident. I know full well how hard that is and how much grit it took you to get to where you are today. There are no hard and fast rules concerning nay of the volume recommendations we make. We provide the percentages of previous years as suggestions only. There is too much interpersonal variations
With that said:
As for initial training volume for you with your very high pervious level of training I’d try starting at the 50% of your average when you are last training. Start with 7.5hrs of aerobic work/week and see how that feels for a few weeks. With your background in training you’ll know pretty quickly whether is is too much. Be very cautious about bumping up volume int he early weeks till your body gets used to the routine.
As for maintenance work. Many of use have to do extensive rehab/maintenance work just to get our the door. Trust me, you will too from here on out. While it does take time, I don’t think you should count this in your training hours. It will help you be able to train but will not really contribute directly to fitness gains unless you are at a very low level.