How often you need to file the VAT return?
It's 4 times(for the 1st quarter by the 25th of April, 2nd quarter by the 25th of July, 3rd quarter by the 25th of October, and the 4th quarter by the 25th of January) for a corporation or 2 times(for the 1st half year by the July 25, and the 2nd half year by the Jan. 25) for a sole-proprietorship, it's quarterly or half-yearly respectively.
But for the sole-proprietors who need to reduce those interim VAT tax payment (need to pay by April 25 and Oct. 25), they can file the VAT return if the amount is quite a bit different with the previous return.
Just file on due date is important since there will be 20% penalty if you didn't file on time.
More details, please send me an email to email@example.com, gooday!