SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '503b4cb46dcbe6d5879c6ffc6ee3a5d488b3fe4dfc077f15346038e1d85c6a37' 
  AND token = 'HGdw7LZmomXVJFCkzpYCfZxO8YivItB/uNFIdyKv954=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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