SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '81fcf02ff27a5a09a44298adda7c31fb9957e060a956be902404b82e65da5c23' 
  AND token = '0k1OZIWEoum9qnTJYXKLr5qofm9BOEjqgzGhrEFqxuI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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