Those times seem very odd to me, and as you point out they do not add up to the 9 hours that economy 9 is geared around. I did have a conversation with somebody in the EDF tariffs team about 3 years ago and they told me that economy 9 would not be offered to any further customers as its is the least profitable of the tariffs they offered and had been phased out.
Anyway for comparison I am on EDF Economy 9 Tariff DD.
The daily charge is 27.71 pence.
The low rate is 4.95 pence.
The high rate is 11.72 pence.
The last bill was the winter qtr so always stands out.