Yes, it seems is shorter code but the operation every cycle could make it slowest.

I tried this code in my vscode, and took one of the inputs of the test '86399' and the output was '23.99972222222222:59.98333333333335:59'
So I guess this code is not working right.

I made this just for check the outcomes in a range between 0 and 49:

for i in range(50):
print("For ", i, "Digital root: ", digital_root(i))

if you just leave the "or n" and don't put there the "and 9", the numbers that are divisible by 9 greater than 9 (18, 27, 36,...) will return themselves without adding their digits. Do the excercise and check it for yourself.

I took me some google searches about precedence and read other users replies to understand how the code works.