Compare the whole task, including the review
Recording a sentence is only one part of the job. Include the time needed to find the right record, understand the proposed wording, correct it and hand it to the next person. A fast transcript can still create work when the reviewer has to search elsewhere for context.
Choose one repeatable task and compare it with your existing process. Note which steps become easier, which still need manual work and which depend on another system. This is more useful than timing a prepared sentence.