49 C.F.R. § 7.35
The twenty Federal working day time period in which to render an initial determination will proceed without interruption except as provided in the following circumstances:
(a) DOT may toll the initial twenty Federal working day time period one time for the purpose of seeking additional information needed to clarify the request. Examples of such instances include but are not limited to:
(b) DOT may toll the initial twenty Federal working day time period as often as necessary to clarify fee issues with the requester. Examples of such instances include but are not limited to: