When importing a watch-only address over `importmulti` with a specific timestamp, the wallet's `nTimeFirstKey` will be set to 1.
I think we should add a optional timestamp to `CWallet::AddWatchOnly()` and use it when importing addresses or pubkeys.

{
    if (nOrderPos == -1)
        return;
    mapValue["n"] = i64tostr(nOrderPos);
}
struct COutputEntry
{
    CTxDestination destination;
    CAmount amount;
    int vout;
};
class CMerkleTx
{
private:
  
    static const uint256 ABANDON_HASH;
public:
    CTransactionRef tx;
    uint256 hashBlock;
    /* An nIndex == -1 means that hashBlock (in nonzero) refers to the earliest
     * block in the chain we know this or any in-wallet dependency conflicts
     * with. Older clients interpret nIndex == -1 as unconfirmed for backward
     * compatibility.
     */
    int nIndex;
    CMerkleTx()