SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '721ca154e0d1fbace69a45c95baf762d4451b5ac26bc768019b0ddaae859f04b' 
  AND token = '4GY9QOfmWZiLQbpt3QyEXmwlv6tNIJZ/+t9gUxKuha4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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