A: Ah, rules, rules, rules. I'm not familiar with any of the classic playwriting "how-to" texts, and am somewhat distrustful of formulas--especially for comedy. All I know I learned at the feet of Aristotle and at the School of Theatrical Failure. 

Can something be entertaining without a main story line? I suppose (a lot of Robert Altman movies spring to mind) but my experience suggests that a throughline--even a totally artificial one (cf Alfred Hitchcock) is necessary for an audience to invest in the lives they see on stage. Behaviour--funny, sad, peculiar, whatever--just isn't enough. As David Mamet has observed: the only thing an audience cares about is "what happens next? ". And to keep that particular train going, it seems to me you need that hook. "Will Hamlet kill Claudius?" "Will Oedipus find out he killed his father?" "Who shot JR?" Enquiring minds really do need to know.
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Secondly, how do I time my play from the printed page?

I wouldn't worry about this too much. The play will be finished when the characters have done their business. If the business takes long enough to accomplish, you'll have an evening. If not, you've got something shorter. You are creating a story, not typing up pages.
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G'day Bob, thanks for the service. I'm working on an historical play set in the 17th century, and am intrigued by what you leave in and what you leave out . . .

The good bits stay in, the bad bits go. 

. . . Anyway, your thoughts on how to write a vibrant play with an historical setting would be welcome. Greetings from Perth Australia!

Context is all. The task is to create a world where you care about the characters and their situation, and the conflict must obviously ring true to a contemporary audience, and be something that they care about. Most historical plays fail because the writer simply cannot comprehend that all that fabulous research he finds so fascinating doesn't mean a fig to the audience. The best historical drama --say "The Crucible" or, speaking of Australia, "Our Country's Good"--make us care about the people. Burn all the research--all of it--and start telling a story.
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I am working on a play that is contemporary and would be considered controversial by conservative groups. How can I determine where to submit, and which comes first: production or publication?

An issue with which I have some recent familiarity. Our theatre is located in the most conservative part of Canada, and we just mounted Part One of "Angels in America" . A lot of controversy came our way, and it provoked a very interesting--and at times healthy--debate in our community. A happy ending here--we played to 107% capacity and pre-sales for Part Two in the spring are very strong. 

As with submitting any script, I think you should be very familiar with the theatre's mandate and their recent seasons. There is no point, in my opinion, to sending a script to a theatre that has no track record with new work, or, say in your case, submitting possibly contentious material to a company that does middle-of-the-road murder mysteries. 

Personally, I view publication of the script as merely a documentation of the first production of the play. Our library shelves are littered with scripts that no one has produced, and for the sake of our forests, I don't think we need any more closet dramas wasting natural resources. A script isn't a play until it has been produced.
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When you ask a playwright to rewrite part of her script, how specific are you about the changes you want?

Hopefully, we are in the position that we are talking about not what "I" want, but what the script needs. I'm not trying to impose anything on the writer. It's not my play. If the playwright is sensitive to what is going on in rehearsal, problems usually become apparent and together we can identify a way to proceed. It can be very specific: "Why don't we try cutting the last half of Actor A's line, so that Actor B can come in sooner with hers". Or, "we're repeating an emotional beat in this section that the audience has already experienced: don't you think we can lose these three pages?" Or "These three scenes are redundant. It's just back story that keeps us away from the action." 

Or, my notes can be quite general. "I fell asleep in the second act, and I didn't wake up until the train wreck. Is there something going wrong in these twenty pages?"
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Also, what do you do when you and the playwright can't agree on the kind or degree of script change that is needed?

I can be very persuasive. A large stick also helps. Ultimately, the playwright always "wins". I've agreed to do the play, based on the draft that I first read, and if changes don't happen there is not much I can really do. Short of withdrawing from the production, or suggesting to the producer that the play be pulled, we have committed to presenting the play. If I'm proven "right" by the reception of the play by the audience, then clearly I wasn't the director capable of convincing the writer of the correctness of my choices. Chances are I won't be working with that writer again
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If you're directing a new play that doesn't work, will you try to "fix" it in your production?

You bet. A carefully timed nuclear explosion always comes in handy. As a director, my ultimate responsibility is to the audience, and they deserve the best that my talent and that of my collaborators can provide. The "fixes", though, rarely conceal the dross. But one can pretend.