How many hours do you typically spend standing per day?

Typically about 60-70% of the time standing. I try to stretch every hour or so. I also shift my standing position quite a bit, from a wide stance to a normal stance. When I'm thinking or watching a video, I march in place. Whether standing or sitting, I try to not be any one position for more than an hour at a time.

Do you wear shoes while standing on the gel mat?

Barefoot, since I work at home.

I've been standing at work for several months and prefer to be barefoot as well even without a gel mat.