to answer all of this. However when it comes to breeding snakes, 1 snake will always be different from the next.
With that in mind...
How long does ovulation last?
Depends, how soon can you notice the ovulation? Some females ovulate a lot heavier than others. Some ovulations can be so subtle, you may not see it at all. Other females my not ovulate at all. My personal experience from this past season, my female argentine was swollen for a good 3.5 weeks. She is a very large girl, so I noticed it right away. Also, keep in mind that just because there is swelling, does not necessarily mean ovulation, there is a Pre-ov swell, followed by the actual ovulation swell which is even larger than the pre-ov swell. Very difficult question to give a definate answer.
You asked how can the male be inticed to breed without dropping the temperature?
Everybody has their own method to breeding. Some drop the temps, others choose not to. What I have come to conclude by talking around, find what works for you. if you can get snakes to breed without changing the temps, more power to you. I have heard success stories both ways. The males are like humans, very easy to temp to breed. Put a female in their view, and they will normally go for it. Whether or not the female is ready should be the bigger concern. When I say "ready," I mean is she old/big enough, have enough good weight to her, and if you play your cards right, she should be on the brink of going in heat, which will drive the male crazy.
Birth 120 days after ovulation?
again, depends on the ovulation, if you can accurately count the days, which is not easy. Generally speaking, from the ovulation, 123 days or - 5 days (as posted in a book by Jeff Ronne) should be about the due date. However, if you keep an eye on the forum regularly, there was a post earlier this week about a female being 150 days. Just a waiting game.
and by the way, a wood-chuck could chuck as much wood as a wood-chuck could chuck if a wood chuck could chuck wood. or something like that.
