Objection to additional time was also made earlier in the day when Sen Cornyn was speaking. I think the objection was made by the new Alaska senator who was presiding officer. When Senator Cornyn questioned him on the reason for his objection and pointed out that no other Senator was in the chamber, he withdrew his objection.
This looks like presiding senators may have been instructed by leadership to limit time for speakers. Petty attempt at payback for Senator Corburn requiring them to read the Sanders amendment. Childlike, but certainly in character for Senator Reid and his leadership team.