The Oirase walk is about 13.5 km long - which is about 8½ miles. Even if you were to walk it one way and take the bus back, that would leave next to no time to see Lake Towada. So if you are going to take the trouble to go there, an overnight would make more sense.
You also don't say anything about the rest of your itinerary - if you are starting in Hokkaido, or need to return to Tokyo at the end or anything. All of that eats up more time as well.
If you have time though, seeing Hirosaki is a great addition.
I have been to Oirase Gorge in winter and we drove all the way to Aomori and spent a night there, because it seemed like there were not much things to do at night. It would be a nice idea to stay if you would like star watching or early morning hike.