Hi Andrew,
While I am in a completely different area and market, I do believe I have some decent insight for you.
The answer to your question is heavily dependent on multiple factors such as being a good manager of things generally speaking, how well you do your tenant screening, how comfortable you are with bookkeeping (if you are going to do it yourself), if you have a good selection of service providers in the area etc.
In general I would say that if you are comfortable with bookkeeping, do a good job screening, you have a property in good condition, and you take the time to properly educate your tenant on communication and maintenance procedures, expectations of both parties, and responsibilities, you'll have no problem self managing 1 duplex on your own with very little time dedication.
Typically you will probably spend 15-20 min a month on bookkeeping and entering transactions, and that is about it. The things that will consume more of your time will be maintenance calls and/or coordination (these don't happen every month, especially in a good property with a good tenant), communications with tenants about lease renewals or violations, and of course evictions (hopefully you can avoid these of course). If you are doing maintenance yourself, it can be quite time consuming, and frustrating if you are a busy person with little handyman experience/capabilities. If you outsource your maintenance, the key will be having a good network of easy to deal with service people such as Handymen, Plumbers, Electricians etc.
For tenant management, I use RentRedi and think it is very useful. It allows you to collect rent online via bank transfers which tenants can set up for automatic payments. They can also submit maintenance requests through the app and include a short video and description, which you can the forward to the appropriate service provider to start the coordination to get the issue resolved.
Lastly, if you want to be involved as little as possible, consider hiring property management and bookkeeping. This could end up being time consuming as well so be sure to interview and do heavy due diligence on a property manager before hiring, I am speaking from experience! I am currently transitioning into self management of my small portfolio because I think I can run it better and dedicate less time to it by running it more efficiently eliminating many of the current problems I am facing. I am in a small market with limited options for management.
Hope this helps!
-Kole