If you were a mouse, with human intelligence, could you escape from the lab?
The first step is getting out of the cage. Since mice can't really power their way out of a cage, you'd probably have to wait for a dumb human to pull you out. Cages are normally opened when transferring mice, or during experiments. Animal facilities are well sealed, so you wouldn't want to make your break during a cage transfer. This leaves experiments.
Many experiments start with anesthesia, usually injected i.p. When I do injections, I often just let the mouse sit on top of the cage for a second before holding it down. This would be the time, as a mouse, to run for it. If the human is more diligent - she doesn't let go of your tail for a moment - you'll have to bite her, and hope she lets go.
Once you're out of the cage, the next step is to get "down the floor, and out the door," as my Dad used to say to get me out of those house to school. Having never been a mouse, nor read the relevant scientific literature, I don't know how far a mouse can fall without injury. Let's estimate 50cm, or about 1.5'. The counters in my lab are about 1m tall, so you'd need at least one step in between. The best opportunities would probably be garbage cans, partially opened drawers, or stepping stools. The Carleton lab has a rolling paper towel cylinder that's about 50cm off the ground, which could work as well. You could grab the towel, then jump to the floor like Rapunzel.
Of note, when running as a mouse, it's best to stick to the edge of the room, and keep your tail close to your body. Tails may be good for balance, but they're even better for getting grabbed.
Now you're on the floor. Hopefully, your former handler is freaking out, rather than being mindful and closing the door. You need to break for the door, hopefully under the awnings of drawers or refrigerators. Time is essential here, since a closed door means a short trip back to the cage, and a vengeful death.
Once you're in the hallway, you can afford to be more patient: no one can lock down a whole floor of a building. The next goal is getting out of the building. As a human, stairs would be the best way to avoid detection, but as a mouse, you probably don't want to climb down flights stairs, even if they're only 10cm each. You must take the elevator. But you don't want to go down the elevator now, in the middle of the day, with people around. No, you should wait until evening when the maintenance people arrive, with their lumbering wheeled garbage bins that you can hide under.
So you're in the hallway, and want to wait until evening before riding the elevator to freedom (a rodent Underground Railroad, if you will*). You need to hunker down. In the US, this would be difficult, as the hallways are just walls and doors. But here, in Geneva, you are in luck! Space is so valuable, they put lockers in the hallway, but the lockers don't snugly fit their niche. As a black mouse (oh please don't be blanche or agouti!), you should be inconspicuous. There you can make your souris refuge.
As a Maus without a watch, you'll have to be alert for evening's onset, namely a janitor and his cart trundling by. As he passes, scurry out, and use the garbage cart for cover; you may even hitch a ride, if you dare. You'll need to be a little lucky, and hope he takes the elevator directly to the basement. From the basement you are almost free! Be calm, find a nook, and wait for the humans to dwindle-dawdle off. Then saunter to the garage doors, find a gap, and slip into the world. Now instead of running from humans, they will run from you! Only now you must worry about other, more primal predators.
* Ok, that may have been too much.