How do I import an Electrum wallet into BitcoinJ?
As stated in https://bitcoinj.github.io/working-with-the-wallet:

"The “watching key” in this case is the public form of the BIP32 account zero key i.e. it’s the first key derived from the master."

I also thought it was the master public key, but it is the first (or 0th) derived key.

Hope this helps.

EDIT:

To answer your last question, the seed's creation time is used as a hint to BitcoinJ as to when it should start searching for transactions. If you have access to your first transaction on your Electrum wallet, use that approximate time.