ESA 7 day waiting period

I have a client who has reduced her hours at work to enable her to claim ESA.

Assuming there is no backdating, would the 7 days waiting period start from the date on the fit note, date of the claim or date she reduced her hours at work?

You may need to expand the question a bit but waiting days are the first 7 days of the award, so it will be whenever she claimed and met the entitlement conditions for ESA from. The first 7 days are self-certified but beyond that the date when she reduced her hours may be relevant to the date that she met the entitlement conditions, if she had made the claim by then.