I don't know where that "3 minute" rule comes from. It smells like the "you are allowed to download these ROMs only for 24 hours" nonsense that emulator sites (used to?) say. That only increases my suspicion of this advice.
The 3 minute thing seemed to me a simple example of "keep it short to keep viewer attention".
EDIT: maybe you interpreted GP as meaning take a screencast of the code, while I am thinking of the working app?
This isn't like showing off the feature you wrote for MS Word.
Call it a wash.
You aren't supposed to take private work materials with you when you leave. I know for a fact that I've seen "screenshots" explicitly listed as one of the things I'm not supposed to take in several very reasonable employee agreements I've received over the years.
Having been presented with very unreasonable employee agreements (once a security company tried to get me to sign "we own all your IP while you work here, and for a year after you leave" agreement), that doesn't mean the company doesn't get to keep the private stuff it owns private.
It's theirs, not yours. You signed an agreement not to take it. Don't take it.
I guess my point is try to look for resources your company puts out before trying to create your own