The amount of "time out" during the weekday while working from home shouldn't measurably differ from what you did while in the office - that's really your benchmark.
The plus side to the WFH lifestyle is that you no longer need to spend time commuting and that you're able to spread your working hours out a little.
I personally start my working day at roughly the time I used to start commuting and end it when I usually came home.
During those extended working hours, I'll swap around how to build breaks in - walking the dogs, running a quick errand etc. My work colleague all run the same kind of schedule so that we know that if we don't get an immediate response to a request, it won't be long until they get back. Obviously, scheduled meetings are respected.
The key thing is "flexibility". No one expects you to be locked to your keyboard for the entire working day and you really do need some time to get away, refresh, and maintain your mental health.
If you feel you need to time-manage your breaks, then put this into your calendar so that you (and your colleagues) know when it's your AFK time.