All right, this looks like a bit of a project. So let's dive in.
First, if you can't pitch your concept in a three-sentence paragraph, it's too convoluted. You can broaden it as the actual story unfolds, but there needs to be a simple but engaging foundation. What is the theme? What is this story REALLY about? That's what you need to nail down. Often it comes in the form of an abstraction: love, revenge, redemption, etc. Once you know this, you've got a good jump on motivation.
That said, you need to SLOW DOWN. It sounds like your standing over the kettle and chucking assorted spices with reckless abandon, hoping that the bubbling conconction tastes like something recognizable as stew. You really need to scale back and prepare. Who is your main character? What do they want? Start there.
Good stories start with good characters, not cool concepts. That comes after you've humanized your cast.
That said, a character's motivation is what makes us empathize with them--even a sympathetic villain. And if your villain's motivation is boredom, guess what? We feel bored. Boredom is a motivation for comedy, not drama. Give your villain something real. Something strong that we can latch onto. Here's why, and this is VERY IMPORTANT:
MOTIVATION DRIVES ACTION.
If your motivation is boredom, you've got nothing driving the action! The least motivated a person can get is literally a desire to do... "whatever."
Now that I've addressed what I believe to be the heart of your problem, I'll get into the other stuff. The concept, convoluted as it is, does sound cool. Don't mistake that for "ready." Let's try this:
"After a grizzly murder, a group of scientists stumble into a time rift that forces them to return to a critical moment over and over. They can change the course of time, but the only way out is to discover the identity of the killer--who may be closer than they think."
That's about as simple as I can make it, so that it's easy to understand and pitchable.
As far as the villain's motivation, given the scenario you've outlined, it seems the simplest solution is this: One of the scientists (the murderer) wants credit for the technology all to him/herself. Now, if you want to really spice it up, have other members of the group start getting murdered with each consecutive jump back in time. Now you have another important part of storytelling-- "WHAT'S AT STAKE?" And suspense.
The motivation for the scientists as a whole for creating the technology could be to retroactively prevent murders. A tool for good, but one of them is corrupted by the power. Now you have another great part of storytelling: DRAMATIC IRONY!
I do hope all of this has helped. Just scale it back and rebuild it with your characters foremost in mind. Find out what makes them tick before you put them in any real situation, or you won't know what they're likely to do in that situation.