I'm not sure if this is on topic on meta but we don't have a meta-meta to ask whether it is appropriate to ask this on meta. Anyway my question is the following:
How much time do you spend on average on Physics SE per day?
It's very variable. I check the questions in the morning, at lunchtime and in the evening, but how long I spend on the site depends on whether any of the questions catch my eye.
It can take a surprisingly long time to write a thorough answer, especially since the answers that are most fun are the ones at the edge of my knowledge, so I have to spend time researching them. It's not unusual for me to spend an hour on an involved answer. Some of the canonical Q/As I've written have taken a day or more, but that's a special case as it's more akin to writing an article.
I suspect the reason we so often see experienced site members posting brief answers as comments is because it can take such an investment in time to write a proper answer. I trust the OPs appreciate just how much effort is put in on their behalf :-)
Just take a look at the stats page of each of the review pages (or my 4 Steward badges) and my Marshal badge and you can see how I spend most of my time on Physics.SE (which is also a subtle hint for those with 2k+ rep to start reviewing what you can & those with 3k+ rep to start reviewing the close queue).
I usually spend about 20-30 minutes in the morning (while cooking breakfast & drinking coffee) on the (Android) mobile app looking at questions that were posted (trying to manually review, since there isn't a review page on the app) and voting up/down as I see fit. I typically spend another hour or so in the afternoon (during the kids' nap time) and at night (after the kids' bed time) reviewing and answering/commenting what I can. All tolled, that's between 2 and 3 hours per day and less on weekends that I actually spend time doing things on the site.1
Like John, if I find a question that interests me I'll think about the answer for a bit (usually while reviewing and doing daily duties) and spend at least 20 minutes writing one up (usually longer if I need to find links or if the wife and/or kids need attention)--this number is subtracted from the time spent on reviews, so the net 2-3 hours is the same.
1 The numbers quoted here are for my active time on Physics; the tab is open in the background in my browser always, so once the computer is un-suspended (re-animated?) I'm technically "on." In this case, the number is probably closer to 6 hours a day (and longer when I was still a student working 10 hours days).