ESA 6 month rule - when does the 6 months start?

Re the present rule whereby a fresh claim for ESA can be lodged 6 months following a Fit for Work finding -

When does the 6 month period begin?

Is it the date when the DWP originally found the claimant fit for work?

Or, in cases that go to appeal, is it the date when the tribunal upheld the DWPs decision?

Be grateful for clarification on this.

It is the date of the first decision that counts.