根据场景需求需要对已存储得数据做更新查询，所以需要对update_timepoint做查询索引

struct [[eosio::table, eosio::contract("bcskill.com")]] xxxx_info {
        uint64_t id;                                        // 记录id
        eosio::checksum256 trx_id;                          // 交易id
        ....
        time_point create_timepoint;                        // 创建时间
        time_point update_timepoint;                        // 更新时间

        uint64_t primary_key() const { return id; }
        eosio::checksum256 second_key() const { return trx_id; }
        uint64_t third_key() const { return update_timepoint.time_since_epoch().count();} // 把time_point类型转换成微妙（1/1000000 秒）
    };

table中测试数据如下

{
  "rows": [{
      "id": 0,
      "trx_id": "d78c4da408a4d9c75ba03af4a481d79fa80e2b8e215e68a1fe1865fd866cc7bc",
      ...
      "create_timepoint": "2020-12-17T11:24:07.500",
      "update_timepoint": "2020-12-17T11:27:18.500"
    },{
      "id": 1,
      "trx_id": "7bb0038be49b171f8a394bfdd7da15f9a005908b25ca1b6aed31b2975d721730",
      ...
      "create_timepoint": "2020-12-17T11:29:01.500",
      "update_timepoint": "2020-12-17T11:30:01.500"
    },{
      "id": 2,
      "trx_id": "8cf1c32d38692dd93870c7a2376d617f85efa4f093588dbce94f9981d4e1818e",
      ...
      "create_timepoint": "2020-12-17T11:30:01.500",
      "update_timepoint": "2020-12-17T11:30:01.500"
    }
  ],
  "more": false
}

UTC时间转时间戳，目前没有找到现成的工具可以直接转换，
https://tool.lu/timestamp/ 只找到这个北京时间转时间戳的工具（稍后找到其他直接工具，或者单独开发个工具再做文章更新）

UTC 转北京时间（+8）

暂时先将UTC时间加8小时转换成本地时间，测试的UTC时间为2020-12-17T11:27:18.500，转换为本地时间为2020-12-17 19:27:18 其中的.500为0.5秒，后面再单独加上。

北京时间转时间戳

利用上面的在线工具2020-12-17 19:27:18得到1608204438，加上上面的0.500得到1608204438.5

根据合约类型需要转换为微妙

1608204438.5 * 1000000 得到 1608204438500000

根据测试数据演示下查询

cleos get table bcskillsurou bcskillsurou ammtb --index 3 --key-type i64 -L 1608204438500000 -U 1608204438500000

得到指定的记录

{
  "rows": [{
      "id": 0,
      "trx_id": "d78c4da408a4d9c75ba03af4a481d79fa80e2b8e215e68a1fe1865fd866cc7bc",
      ...
      "create_timepoint": "2020-12-17T11:24:07.500",
      "update_timepoint": "2020-12-17T11:27:18.500"
    }
  ],
  "more": false
}