That's amazing. Have you looked up whether this ability has been observed in other dogs? Do you think your Shiba is counting the days, or maybe there is something different about Thursdays (besides your family member visiting) that's giving him a hint?

My Shiba knows his "spots" where he meets friends of his and what times we usually run into them. And when they miss those times he will lead us to their apartment because he knows which door they live behind. It's crazy.

It's almost certainly something he does subtly different. The timing of making breakfast is different, or he cleans up more conscienciously, etc.

Not that dogs can't figure out weekly rythms, but they're much better at spotting subtle precursor behaviors

Can maybe be something like a garbage truck.

Lucky guess! I take the garbage out on Thursdays :)

I doubt the dog is actually keeping track of the days. Definitely picks up cues from my own behavior based on the day/schedule, like taking the garbage out.

I had a Samoyed when I was a child that knew Sunday. We had a specific routine for him while we went to church. He’d stay in the backyard in his large kennel while we were gone. After not too long we’d wake up Sunday morning and he’d go straight to his kennel. :)

In our case it was probably him sensing other things that only happened on Sundays.