SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21f40118a55c3ecc2d1eb78cc9cd1ab27636637955adad350c7508f8e981744b' 
  AND token = 'SdE/Tp8yFndLMNJURziLu1ctvrnfcjfDSfmfysuTtfM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}