The properties that an IV must meet are strongly dependent on the mode that the IV is be used in. Some modes require unpredictability; other modes don't care about unpredictability but require uniqueness.
As for OFB mode, it's in the 'don't care about unpredictability, but require uniqueness' camp. In particular, as long as you never reuse an IV, and you are unlikely to use an IV that was previously used to encrypt another block, you are secure.
This can be seen by the way OFB works: the first block is encrypted as:
$Ciphertext = Plaintext \oplus Encrypt(IV)$
As long as two different messages have different IV's, their corresponding $Encrypt(IV)$ will be totally unrelated. This holds true even if the attacker can predict which IV you will use.
Hence, to answer your question, deriving an IV from the current date and time would be secure if you never use the same IV twice; for example, the current time always increments between sending two different messages.