I have Fire safety concerns about a building on the Estate that contains 20 storage sheds, with wood doors and frames. There is a single entry and exit door also made of wood. There are no windows in the building or the entry door. The interior is in pitch darkness until the Estate lighting is activated at 7PM. If residents wish to access the building before, they need to use torches.

If it is not a private dwelling then strictly speaking it requires an FRA which would need to be proportionate to the actual risk present. It sounds like the lighting ought to be on sensors rather than an arbitrary time meaning it's only on when someone is there which would solve your issue whilst actually saving money by having on continuously from 7pm even if no one is there.
Obviously some of the light fitting might need to have emergency packs as well.