It sounds to me that Timber would have the best of both world's, I cannot see a big problem with it, maybe you could tell you Aunt to give it a trial period first, to see how Timber adapts and if all goes well, then continue with it.

My girlfriend down the road from me, has a good thing going with her neighbour, he is away at work all day long,so Duke lives at her house as she is home mostly, he goes everywhere with her during the day, and at night pops home to his owner's he does not seem confused at all, and best thing is he is happy and content, and not lonely and my friend has a dog without all the pet expenses, so going on that I cannot see why it would not work.

Good luck with whatever you decide, you will know what is best for Timber.