You wake up. It is pitch dark. You don't know where you are. You feel groggy.
The last thing you remember is being in a bar, a sexy young woman appeared out of nowhere, walked straight at you, smiled, engaged conversation and offered you a drink. You should have known things don't happen like that. You should have been suspicious when she complimented your outfit and started to laugh at your math jokes. Anyway.
You must have been kidnapped. Now you are in a prison cell or something, behind bars. It is pitch dark.
You wonder what time it is. Is it day or night? You have no idea. There are no windows.
You don't wear watches any more. But you still lift your wrist. Old habit. Anyway it's pitch dark, you don't see anything. And your smartphone has been taken away.
You just sit there and look into the darkness. Did I mention? It is pitch dark.
Then you notice, outside of the cell, there is a faint reddish glow changing slightly every second. There must be a digital clock on the wall, but invisible from where you are. The kind with luminous 7-segment digits.
You are bored. And you really want to know what time it is.
The faint glow changes slightly every second. It must be the number of segments that are lit at any time. Sometimes it doesn't change. You can't tell exactly how much it changes or how it compares to a few seconds ago. You only see whether it gets brighter or dimmer. Every second. Mesmerizing.
You realize you probably can read the time from that.
The question: Is it possible to eventually know the time from the changes in the reddish glow? If yes, how long will it take in the worst case to be certain what time it is?
Assume 24 hour format. But does it display a leading zero on hours? You are not supposed to know. How would you, right?