It depends on the intensity of the dissertation paper. As per the doctoral dissertation, it might take about 2 weeks for approximately 25,000 words to expertly proofread and edit an economics dissertation. If the dissertation is long then the editing time might take longer for doctoral-level to make it error-free.
A dissertation editor or proof-reader thoroughly checks each section of the dissertation. An expert dissertation editor is able to correct errors of grammar, structure, formatting, punctuations, spelling and much more. It is the duty of the dissertation editor to mention the mistakes and edit them to make a dissertation flawless.