Republican senators decided to relax the schedule during a lunch on Tuesday just before the trial was gaveled to order. That left the Republican-controlled chamber to consider a set of procedural rules that were hurriedly revised by hand, there being no time to reprint the formal resolution.
Minority Democrats had complained bitterly that the original plan, which could have meant 12 hours of lawyers' opening statements each day, "could force presentations to take place at two or three in the morning ... literally in the dark of night," as Senate Democratic Leader Chuck Schumer put it.
Republican Senator Mike Braun acknowledged lawmakers' personal comfort had something to do with the Republican climbdown to a somewhat more relaxed schedule. After sitting through the preliminary trial motions on Tuesday, he told reporters, "I don't think I'd be as apt to say I could sit through 12 or 14 hours or whatever it might be."
The new plan allows up to 48 hours of opening arguments over six days, instead of four, from the House of Representatives lawmakers making the case for impeachment and Trump's defense team. The trial is set to start each day at 1 p.m. (1800 GMT).
Democrats have called on the Senate to remove Trump from office for pressuring Ukraine to investigate former Vice President Joe Biden, a political rival, and then impeding the inquiry into the matter. Trump denies any wrongdoing.
Republicans on Tuesday also agreed to change the proposed trial rules to allow the House record of its impeachment inquiry to be automatically admitted into evidence. The Senate was expected to approve the plan for the trial later on Tuesday.
Braun said Republicans decided the changes at lunch and presented them afterwards to McConnell, who had left early.
"It was pretty much a (Republican) conference consensus that that made a lot more sense," said Senator Ron Johnson, another Republican.
Those who expressed concerns included Senator Susan Collins, a centrist and so far the only Republican to say she is likely to support calling witnesses. She was concerned the more aggressive timetable and evidence rules originally proposed by McConnell did not follow the model of the impeachment trial of former President Bill Clinton, a Democrat, two decades ago. Clinton was acquitted.
"Her position has been that the trial should follow the Clinton model as much as possible," said Collins spokeswoman Annie Clark.
The changes marked a rare climb-down by McConnell, who had only unveiled the proposed trial rules on Monday night. "Obviously he’s willing to take feedback," a McConnell spokesman said.Senator Richard Durbin, the Senate's No. 2 Democrat, said of the Republican revisions: "When you're hanging onto an indefensible position, you quickly abandon it."