Question for you...back when the Dems controlled the Senate for years, and had huge majorities..( I think one year it was 70-30 or so, was floor time EQUALLY divided between the majority and the minority?
That would be a tough one to research, lots of gruntwork! But I think the protocol is that time is equally divided between the PROPONENT an OPPONENT sides of a measure, amendment or motion, and opponent/proponent does not devolve to party line.
The opponent/proponent line can be fun to watch in practice, as a Senator can crossover from the nominal party line on any given issue.
If a time agreement is operating, the debate time is divided between the majority and the minority managers for the bill. The floor managers are usually the chairman and ranking minority member, respectively, of the committee which reported the bill to the Senate floor. Senators must seek time to speak from their floor manager who manages the time for his/her side. During this period of "controlled time" in the Senate, you will hear rare references to time limitations, for example, "the Senator is recognized for 15 minutes," or "I yield 7 minutes to the Senator from Kansas."http://www.c-span.org/questions/week117.asp
controlled time - When a unanimous consent agreement limits the time for debate on a bill or other measure and places it under the control of bill floor managers, the time is said to be controlled. Each manager then allows any Senator to participate in debate by yielding a specified amount of time to the Senator.http://www.senate.gov/reference/glossary_term/controlled_time.htm
yield time - When the Senate has reached a unanimous consent agreement limiting the time for debate and placing it under the control of floor managers, a Senator may be recognized to speak only if a manager yields the Senator a specified amount of time to speak. The Chair then recognizes the Senator receiving the time, not the manager who yields the time, to hold the floor.http://www.senate.gov/reference/glossary_term/yield_time.htm
Any limitation on debate (and hence impacting the division of time) can occur only within a unanimous consent agreement. Riddicks talks of debate under a UC Agreement, and uses both terms "time divided and controlled" (p. 1323) and "time equally divided" (p. 1324 and following). If a new amendment is introduced within the time agreement, Riddicks says at p. 1323, "if an amendment is considered under its own time limit, the time consumed from that particular sublimit of time will be equally divided and subtracted from the overall time available to each side on the measure."The general arrangement of this section of Riddicks reads as though the time could, by unanimous consent, be divided other than equally. For example, at page 1327, "when the Senate is considering a matter under a unanimous consent agreement which limits and assigns control of time, and no Senator yields time, the time expiring and otherwise available for debate will be deducted proportionately from those controlling the time.
Ahh ... a short and sweet authoritative source. All emphasis herein is mine.
Debate Time. Consent agreements that include limitations on time available for debate are also called "time agreements." A time agreement may establish an overall limit on debate of a measure, or may regulate only a certain day or portion of consideration. Usually, it specifies a length of time for debate of a measure, "equally divided and controlled" by the majority and minority bill managers. Occasionally, other Senators may also control blocks of this "bill time," or it may be divided unequally among Senators controlling it. When time on a question is controlled, a Senator can be recognized to speak on that question only when a colleague who controls time first yields a portion of it to the Senator. Also, until all time on a question is used or yielded back, no vote can occur on the question, nor can an amendment or motion to table be offered.Here is a link to CRS 98-225, the general case referred to in the publication linked above.How Unanimous Consent Agreements Regulate Senate Floor Action
Richard S. Beth - Congressional Research Service
As to how the actual practice breaks down, and in particular whether the DEMs took advantage of their majority status to shortchange the minority from debate time, I don't know.