The objective of that is to prevent the president from making any recess appointments.
The Republicans (actually, any single Senator) have the power to object. There being no objection, the schedule was agreed to.
The Democrat leadership of the Senate has been filling extended breaks in legislative action with pro forma sessions (with the same purpose) for a year or more.
And if Republicans had been doing it to stop Clinton recess appointments, it would be discussed on news programs every day.