SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '861378b8c7ffa602c3881f9d54fcac69a8efe3c173fb39986ea7aecea9f109fa' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.35"
    },
    "table": {
      "table_name": "cscart_lock_keys",
      "access_type": "ALL",
      "rows_examined_per_scan": 1,
      "rows_produced_per_join": 1,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "0.25",
        "eval_cost": "0.10",
        "prefix_cost": "0.35",
        "data_read_per_join": "392"
      },
      "used_columns": [
        "key_id",
        "expiry_at"
      ],
      "attached_condition": "((`mobikul_delivery_boy_livedemo`.`cscart_lock_keys`.`key_id` = '861378b8c7ffa602c3881f9d54fcac69a8efe3c173fb39986ea7aecea9f109fa') and (`mobikul_delivery_boy_livedemo`.`cscart_lock_keys`.`expiry_at` > <cache>(unix_timestamp(now()))))"
    }
  }
}