If you bought a clock and hung it on the wall...

took my husband about 6 weeks one time. it was hanging in the entryway, not exactly hidden!

Many years ago, I wallpapered the laundry room while DH was on a business trip. One must walk through the laundry room when entering/leaving the house via the garage (which is how we enter/leave 99.9% of the time).

The paper was very colorful. With stripes. And a border. On all four walls.

DH didn't notice for months.

I'm not complaining, as this works to my advantage the majority of the time. I do lots of cool things while he's away on trips.

I replaced the plain hallway light fixture with a stained glass one. It took well over 3 months for him to notice. This hallway is between our kitchen and family room. And while we rarely use that light, he probably walked through there a couple hundred times.

Several weeks. Maybe. Or it might take a year. He's absolutely oblivious to things in the house. He's also oblivious when I change my hair color. To him, it's ALL visual clutter. So he ignores it all. It's amazing what he simply doesn't notice. He'd be a terrible witness.

That's why I no longer compromise with him over home furnishings. He'd argue til the cows come home to get his way over the color of our bedspread and then could not tell someone what color the bedspread is. No lie. Seriously, no lie. So I don't compromise any more. I just go out and buy what I want. If he's going to be oblivious, he can be oblivious to my choices and I can be happy.

My DH notices everything.  Every little detail.  I, on the other hand, would take weeks to notice something like that.  I just don't pay much attention to my environment.  Especially in my own house because I am so used to everything being wherever it goes.