Although I won't be able to attend, I would vote for Jack Chalker or Orson Scott Card.
Actually, since I am an old coot, I really would prefer Isaac Asimov or Arthur C. Clark. Impossible, I know, unless one of the time travel experts could get them there.
BTW, I am currently reading Winter's Tale at your recommendation.
Without a doubt...Greg Bear. Runs or has run with many Grand Masters of Sci-Fi including Heinlein, Clarke and Asimov. He wrote a Foundation book for goodness sake...how many get chosen to do that?
Has written Halo, Star Trek AND Star Wars books and wrote one of the absolute hands down BEST hard sci-fi books of all time...EON (The Way is mind blowing!!!) Nebula award winner...nominated numerous times for Clark, Hugo and other prestigious awards...this guy ROCKS sci-fi. If you haven't picked up a Greg Bear book...run to your local laptop and hammer Amazon for one or forty.
Could easily see him being designated a Grand Master someday.
My favorite sci-fi book ever remains John Wyndhams's Day of the Triffids. the BBC did do a series on it back in the 80's, but it was thoroughly rubbish and the "special effects" were super lame. I wish someone would remake that one properly.
As for traveling through time... my favorite episode of star trek was the "Stone knives and bear skins" episode (Star Trek Classic episode The City on the Edge of Forever)- that has some good ideas about what would be useful and what wouldn't!
And, in terms of Zombies, I really liked I am legend, though it ended a bit weakly in the movie