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.
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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."