Takachiho and Aso by rental one day?

Hello fellow people.
I intend on visiting Takachiho as a day trip as it apparently is not very much to see there except the temples.

Looking at the driving guide it would take a rough 2 hours using the 445 and 218 roads, or the 325, but not sure how accurate it is now with the road closures south of Aso (which it passes).

Returnway says about 3,5 hours passing through Mt Aso ropeway from the north road and doing a detour north of the broken bridge on route 57 west of mt Aso.

Would leave the rental shop as soon as it opens at 8 o'clock.

Is this doable as a daytrip or should I stay somewhere along the road?

I would leave as soon as the rental shop opens at 8 o clock.

I assume you plan on making a day trip from Kumamoto. It should be possible for the typr of person who likes a very fast pace of travel. But for people who prefer a slower pace and see the places in more detail, it will be too much.

I intend on visiting Takachiho as a day trip as it apparently is not very much to see there except the temples.

I am not aware of any temple of interest. Takachiho is most famous for its gorge and Amano Iwato Shrine:
http://www.japan-guide.com/e/e8050.html

Looking at the driving guide it would take a rough 2 hours using the 445 and 218 roads, or the 325, but not sure how accurate it is now with the road closures south of Aso (which it passes).

Yes, the driving times you looked up sound more or less accurate. I would add a little bit time for possible delays. Traffic can be heavy when entering Kumamoto City.

As you can see, you will be spending more time in the car than sightseeing. If that is something that appeals to you, it is doable.

I found a rental shop outside Kita-Kumamoto station as well as one some blocks east of Kumamoto castle, past the river. At least it helps getting away from the most central parts.

I suppose returning back from all possible sightseeing is when the sun sets, though I can't say i fancy driving in the dark.

The gorge does not really fancy that much, I'd more intrest in the religious areas. But if it is too much of a sideway maybe I'd rather skip it.

In case the Aso status changes from level 2 to 3, I suppose that would cut some time but I'd rather see it at least once from the "top" before it cannot be accessed...

In case the Aso status changes from level 2 to 3, I suppose that would cut some time but I'd rather see it at least once from the "top" before it cannot be accessed...

Level 2 (currently): closed one kilometer from crater
Level 3: closed two kilometers from crater

At level 3, you can still access Kusasenri and the volcano museum. There is not much beyond that, anyway (as long as you cannot see the crater).

The "top" becomes inaccessible only beyond level 3, i.e. when a major eruption is expected to occur soon or is occurring. Or when the road there is closed, e.g. due to earthquake damage or snow.

Not much to see in Takachiho?

You need 4-6 hours to do everything. Unless you just get out of the car, take a few photos from the carpark, then drive off again. Then you might do it in two hours.

Then you have the night shows also if you plan you day right for late departure.