There are a couple of trade-offs in using a recirculation system. First, any time you are recirculating hot water when you are not actually going to use hot water, you are wasting energy. You're heating water which goes into the plumbing pipes and starts to cool off. Second, for the type of system that uses a bypass valve, the cold water tap at the bypass valve location will emit the pushed-back water that is warm or hot until it is all expelled. 

You can see from the photo in the previous project log that the Watts unit has a simple analog timer, which is useful for the "popular" hot water times, but it's no good for other times. Even better would be to have the pump read your mind and switch itself on 5-10 minutes before you need hot water. That mind reading is a tricky business. The next best thing is to be able to tell the pump that you want hot water now, and then you just have to wait that 5-10 minutes to get it. That's what I did for my Watts unit. I described that here, so I won't bother to repeat it.

The Navien A2 series has 3 modes of operating the recirculation pump. As far as I can tell from reading the documentation, they are all mutually exclusive. They can't be combined.

• A "smart" mode that watches your hot water usage for a week and then sets its own schedule based on what it saw during that week. I don't know if it adjusts things if your usage changes later.
• A timer mode that uses a configured schedule.
• An on-demand mode, which they call HotButton, to start the pump in response to a button press. The button can be either hard-wired (a simple normally-open switch between two contacts) or a few different wireless options for the same thing.

My plan is to use the on-demand feature integrated with Home Assistant. That integration will not only give me job security in the household, but it will also let me implement any of the other schemes if I see fit. I'm going to start with simple on-demand push button stuff and see how that goes. If warranted, I'll implement the timer mode.