[NelsonMinar]

Also if it's really the date it's nowhere near 32 bits of entropy. I'm guessing you can pretty easily guess to the day when a Bitcoin wallet was created, so that's about 16 bits of entropy. Less if you know the time, possibly 0.

[ryanatdistrust]

It actually uses the most precise 32 bits of the date, so it's any, like, nanosecond between 0 and some other small amount of seconds. You can't brute force a wallet by knowing approximately when it was made, but you can brute force every mnemonic if you have the time or a bit of cash to throw at a server.

EDIT: It loops around to 0 every 4.something seconds, so it's not like everything after 4 is the same key. It's just a more random distribution than what you may be thinking.

[aidenn0]

There is often very low entropy in the lowest few bits of system time as well (due to the underlying clock having a different resolution than the system call). Given that every bit you lose halves the time for a brute-force, that's a problem.