You must return to the time machine at the same instant at which you left. If you don't you will be caught up in a repeating loop of infinity, reliving the same day again and again. This is what happened To Holly Turner's father, and is the reason behind his disappearance.
You cannot prevent events from happening, time will find a way of stopping you. So you can go back and investigate a crime, but you can't stop the crime being committed. This isn't Star Trek!
You can only travel into the past. The future hasn't happened yet!
To get back to the present you must re-live the past, you can't just hop back to the time you left!
If you encounter yourself in the past it could have catastrophic consequences!
The machine can take you back an hour or a week, there is no way of controlling it. However some other scientists working for Steve Marlow had solved this problem, and you could specify how far you wanted to go back in half hour increments.
Time won't let you cheat! You can't place a bet on a horse knowing the result, as the race hadn't run yet! According to time you didn't know the result. It's a paradox..(see transcript for explanation!)
The machine has a timer which beeps once when you have one hour to go and then continuously for the last three minutes. If the clock isn't back on the time machine before the timer runs out, you've got your loop of infinity!
You cannot go back more than once in any time frame. So once you are back at the machine you can't immediately go back again. Time won't let you be in three places at once, besides two is bad enough!
The amount of time which you go back can be controlled by lengthening the photon rods. However as Turner can't afford to get new rods, she can't control the amount of time she and Slade travel. The only time machine that could was the one that Steven Marlowe used in The Broken Crystal and which has since been destroyed.
Whenever the time machine is use anything electrical in the near surrounding area goes barmy! Lights flash on and off and television reception gets decidedly dodgy!
In the heart of the machine is the electromagnetic crystal. It's the single most expensive component, and without it the machine will not work.
The is a stretch of cable that runs across the wall where the windows are. Unless all the window shutters are closed (completing a circuit) the machine will not work.