You folks should read the CRM Debate on the previous forum.
Isn't it bleedin' obvious? Anytime before the wheels touch the ground is OK for a late landing clearance.
If you are unhappy with making a long flare or continuing below a certain height then put your finger on the button and ask the controller to confirm your landing clearance!
Have you never had an instructor tell you that a deer or something has strayed onto the runway?