55.3(d): the boom of a sail may be sheeted to a spar projecting from the boat. [Webster: bumkin]

Is there a reason a finishing window couldn’t be based on the first boats elapsed time plus x%.
I.e. 50% = first boat 60 minutes, last boat 90 minutes, or first boat 120 minutes, last boat 180 minutes. 
The % could be chosen based on the handicap spread of the division - tighter fleet, smaller %, wider fleet = bigger %. 
I think this would solve an issue for my club. We currently only have a time limit of 2 hours for 1st then 3 hours for last. Our winter series can be either cans or harbour courses. The 2-3 hours is really for the longer harbour courses. We’ve had short cans courses lately due to light winds. The first boat has taken 40 minutes, the rest of the fleet done by 50, but one boat who should be mid fleet is off the pace, and took 100 minutes. Wore a bit thin with the start boat, who then got back in the dark, which then delayed prize giving for everyone else, but didn’t break the time limit rule. However, a 30 minute window wouldn’t be big enough on a 2 hour race, but 1 hour is excessive on a 30 minute race (we had one race which only took 20-30 minutes) . Can it be flexible as suggested? Or must we resort to the complicated (for or RO’s) formula / app to calculate? I can’t see anything in the rules. 

Check out Australian Rules Football, Ben. It has everything you suggest including 50m penalties (on a really big field of play); big scores; different scores for a goal (6pts) versus an 'almost'-goal (ie. a 'behind' worth 1pt); and more. It also involves full contact at full speed without the benefit of body armour which makes absolutely no sense to Americans.

BTW, the Irish play Gaelic Football which is close to Aussie Rules, so they sort of "get it". However, they also play 'hurling' which is like "field hockey" played at head height. And for the North Americans here, just imagine Ice Hockey played at head height with no helmets or body armour. In my view the Irish are "feckin eejits" if I was to use their slang.

Rob re: "were to luff sharply and hit the blue boat, the blue boat would protest under rule 16.1 and quite probably win in the protest room"

That's what I'm trying to say (in my typical awkward way) .. that a luff up breaking 16.1 would not be exonerated based upon Red's MR rights.

I'm not saying that Red is not entitled to MR .. she is. I'm arguing (for the sake of the argument ... wiling to be convinced otherwise)  that MR doesn't include luffing to HTW when that luff is not a component of a path to the mark that exists with MR. 

If I was to argue against that point I might argue the following ..

If Red luffs HTW and IF Blue passed HTW first , AND then when Red follows Red tacks such that Red is overlapped to windward of Blue as Red passes HTW (BOTH conditions required to keep MR contiguous) .. she will be the KC boat even if they are both tacking the same time, but Red's MR will change over from 18.2(a)(1) to 18.2(c) .. now being the windward/inside boat.  In that way, there is a feasible path that Red is never not entitled to MR as she tacks for the mark. 

That path though depends upon Blue passing HTW first.

Another argument against might be geometric.  Any time Red is in the 6-9 quad, when she luffs HTW she's shortening her distance to the mark (hypotenuse vs sine).  So that's "closer to" as in sailing past at some distance vs "to" the mark. 

Robert "My review of RRS 86.1(a) indicates no issues with this change."

An argument against that assertion might be that 86.1(a) forbids changes to rules of an appendix that changes Part 2 and Def's and that doing what you suggest .. in effect ... changes those Appx-rules by inserting a "however-clause" exception and then inserts the standard language.