I watched a 2004 movie called "Primer" on Showtime some time ago. It's about two twenty-something men who are working on a machine that manipulates gravity.
They come to realize that the machine can actually transport things through time. The movie deals with the dilemma the men face on how best to deal with such a contraption.
A very complex movie and, at times, hard to follow. I had to go on the internet after viewing it to get a better handle on what I had just seen. I found out later that the film had been made for a paltry $7,000. So much more ambitious and thought-provoking than most of the multimillion dollar junk that comes out of Hollywood these days.
If I could time travel, one of the first things I would do is try to find a way to make it so that large dogs (like Saint Bernards) could have longer life spans.