....many more mistakes of judgement, gets fired because frankly, if I listened to him, we would be in World War Six by now, and goes out and IMMEDIATELY writes a nasty & untrue book. All Classified National Security. Who would do this?

— Donald J. Trump (@realDonaldTrump) January 29, 2020

Politico | 12 questions to expect at Trump's impeachment trial
Conclusion seems to rely on private agreement between minority and majority leaders or an interpretation of Clinton trial procedures, which is not cited.

NPR | Impeachment Trial Moves To Question Phase, While Witness Vote Looms
Does not corroborate Politico procedural assumptions.
--
Neither mentions 5-min. time limit for managers' responses.

Neither contemplates rebuttal by "managers" to each response to alternating questions by senators.

Neither expects the purported "clearing house" (Politico) to order questions submitted by senators dynamically, ie. as pertinent to response immediately preceding the alternate question.

supra
amateur transcript
Congressional Record (pdf, p 9)

Mr. MCCONNELL.  Mr. Chief Justice, I have reached an agreement with the Democratic leader on how to proceed during the question period. Therefore, I ask unanimous consent that the question period for Senators start when the Senate reconvenes on Wednesday; further, that the questions alternate between the majority and minority sides for up to 8 hours during that session of the Senate; and finally, that on Thursday, the Senate resume time for Senators' questions, alternating between sides for up to 8 hours during that session of the Senate.
[...]
The CHIEF JUSTICE. During the impeachment trial of  President Clinton,The CHIEF JUSTICE. During the impeachment trial of President Clinton, Chief Justice Rehnquist advised "counsel on both sides that the Chair will operate on a rebuttable presumption that each question  can be fully and fairly answered in 5 minutes or less." The transcript indicates that the statement was met with "laughter." Chief Justice Rehnquist advised "counsel on both sides that the Chair will operate on a rebuttable presumption that each question can be fully and fairly answered in 5 minutes or  less." The transcript indicates that the statement was met with "laughter."

McConnell recaps. Majority leads with a collective Q submitted by 4 (R) senators (There's a twist!), addressed to (R) managers by COLLINS, concerning MOTIVE

< wipes tears >

The letter from the White House National Security Council to Bolton's attorney, Charles Cooper, and seen by Reuters, said the manuscript contained some material that was considered "TOP SECRET" that could reasonably be expected to cause "exceptionally grave harm" to U.S. national security if disclosed without authorization.

The letter, which was sent via email to Cooper, was dated Jan. 23.
[...]
The letter, signed by Ellen Knight, the senior director for records, access and information security management, said Bolton's manuscript was still being studied.

"The manuscript remains under review in order for us to do our best to assist your client by identifying the classified information within the manuscript," it said. "We will do our best to work with you to ensure your client's ability to tell his story in a manner that protects U.S. national security."