In the past a lot of the non-refundable rates were "cancel within one day of booking" which meant they could be used for LNF booking, and one had time to cancel if the claim was not approved (or responded to in time).
Now I see less of this wording and instead I see (an example for the Berlin Marriott):
Advance Purchase rate, prepay in full
(...)
You may cancel your reservation for no charge until 26 August 2017.
(...)
Does this mean I need to cancel today (25 August), or can I also cancel with no charge tomorrow?