function genEstKeyBlockNr(uint256 _endTime) 
        public
        view
        returns(uint256)
    {
        if (block.timestamp >= _endTime) return block.number + 8; 
        uint256 timeDist = _endTime - block.timestamp;
        uint256 estBlockDist = timeDist / BLOCK_TIME;
        return block.number + estBlockDist + 8;
    }