Yes. Subs that are inside their 10 minute confirmation window are visible to others.
I was of the same opinion as you when I first realised. I haven't really changed my view but I haven't really noticed it being a worry either.
One thing I do recommend is that if you are checking to see if you should attack someone, do it all in the time machine dialled 10-20 minutes ahead. It usually won’t make a difference but it does keep everything a secret until it’s ready to roll. This is especially important if you are planning a backstab.