As far as I know, the NOW operates as needed. Most of the time, that's daily Mon.-Fri., but the times that they are operating each day vary. I've caught them in Tiffin, Maple Grove, Gibsonburg and Helena, Ohio on various days at different times. I grew up in a town not far from Tiffin as well as having an older brother working at a college there, so I have been there many times.
I've never been able to find them in the same place at the same time from day to day, so it's just a guessing game for the most part.
I don't believe that the NOW runs into Walbridge. Last I knew, they interchanged all traffic with CSX in Tiffin, with the rare cars interchanged in Woodville. There is a siding on the west side of Tiffin along the ex-B&O where cars are parked. NOW runs from it's switch onto the B&O near downtown Tiffin out to the siding to pull the cars back to their trackage. Usually, I've found them doing that move in the morning.
There is also a junction with the NS in Maple Grove that has a wye track connecting to their Fostoria-Bellevue line. Usually a handful of cars can be found sitting on the wye track and small siding there. I haven't caught them actually interchanging there with NS, but I have seen them setting out cars on the wye track there. Interesting little junction there, right next to the road with a good sized area to pull off and check it out.
If I had to suggest a time and place to catch them, I'd say start in Tiffin in the morning. If the power isn't there, you can just travel the line north and eventually you'll run into them somewhere between there and south of Woodville.
Best of luck catching this interesting little shortline.