[Grammar] With or without preposition ‘at’

[northpath]

There are two sentences.
The accident happened AT around 9 o’clock.
It happened in the early evening [no prep] around half past six.
Which one is correct or preferable?

 

[bhaisahab]

They are both fine.

 

[Matthew Wai]

I think 'at' is optional because 'around' is already a preposition there.