You mean a report with 2 sub reports? I'm not seeing a need for 2 sub reports but maybe I am not envisioning what you really have. Your main report would be the person details; the sub report the detail records with the time (sum?) for each record. In the sub report you'd group by person ID and total on the calculated field (or total one value, total another value, then in the totals textbox, calculate the sum of A minus the sum of B. If you really have special characters in any names (e.g. #) you really shouldn't. Basically, underscore (_) is the only exception. In the design menu there is a Group and Sort button on the ribbon if you need to turn that on for your report.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.