How to generate a good symmetric secret key
A "good" secret key should have the same probability as any other possible key to be chosen.

No matter what extractor you will be using, if your entropy source is limited to the current timestamp, this is very unlikely to be the case.

Unless you have access to a hardware random number generator, you should combine as many independent entropy sources as possible.

As to the actual entropy collection, answering your question is impossible without knowing what your environment is.