IMO that gong shall always be there for player to use.
As for the range and duration , I think it really depends on the level . In the level I was in the bottom , the road I rly need to walk to is on the top, then I think the duration shall be longer enough for player to acknowledge that "the road is on top , I need to memorize it" , even after they failed, they can look to where they failed , and try to memorize next part.
For the level the gong and the road is in the same altitude , you can test multiple times to see if the you can reach the end while you only needs to follow the sound wave.
I think every one-time item ( In a puzzle game like this ) shall be powerful enough to make it don't need second use anymore , like a gong after you hit , it'll start emit the sound area with an interval or something ,that "you can't hit it again , and you don't have to hit it again".
