SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51741610919ba998e1e289a0a86a3a0ede5722350194022374192322e21f93b7' 
  AND token = '+vaVtnVvHBhjwRom/wOHKjedqqU6VPzgIb2oWwjTEdw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00026

JSON explain

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