OK, this doesn't really match the prompt but it's early in the month and I hope this adds some incentive to your writing. That said, what do you think? I'm thinking maybe some more character development of the young guy at the begining. He's a jerk. And maybe some epilogueish profesorial dialog at the end.
Father Knows Best
The lab was crowded. Much of the empty space was taken up by the half dozen senior physics professors that the young Dr Fynstein had invited to observe the experiment. They sat in a semicircle of folding chairs he had set out.
"Professors. I know the tenure committee has turned down my application but after what you see here today I'm sure you will reconsider." He turned and pointed to the large apparatus occupying much of the lab. "This, Doctors, is a time machine." The group started to mumble and fuss. "I know what you're thinking but please simply observe. For this demonstration I will step into it and disappear for a period of one minute. That is time travel into the future. The machine is also capable of travel into the past but I have not tested that as of yet."
Dr Fynstein threw some switches and adjusted some knobs as the senior professors talked among themselves. He then sat on a chair in the middle of the machine and put his hand on a switch. "Observe please and keep an open mind." He focused on a clock on the wall behind the professors and flipped the switch.
The clock froze. It should have jumped ahead. The audience was frozen also. Then to the side he saw a figure. "What? Who are you?" Fynstein asked.
"Me? I used to be known as Father Time. But those in your profession call me The Cosmic Censor." The figure studied the machine and ran his finger over some components.
"Don"t touch that. What's happening?"
"Roger Penrose talked of cosmic censorship and Professor Hawking postulated a "Chronology Protection Agency". There is no agency, only me." The figure moved some knobs and changed some switches.
"Stop that. You'll damage the machine."
"It's not the machine you should worry about. The universe can't allow time travel. Things get messy. I did allow it once. I can't say that it took me a lot of time to fix it." He chuckled. "But it was a lot of work. I had to create a black hole to contain the damage. Quite useful those black holes. One can hide a lot in them."
"So what happens now? You destroy my machine? Make me forget?"
"Oh, you die. The machine is destroyed in a small explosion. Not enough to seriously injure your audience but enough to discourage them from funding anymore time experiments. You can stay here as long as you want but when you flip that switch again it all ends." The figure faded away.
The explosion knocked the professors from their chairs. They scrambled to leave the room as the flames engulfed the machine and the young scientist.