SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8408daaf929bb5971da566f357672137d41db86b97a4bc65db692736d2c471c8' 
  AND token = '4/sUgM/jTXwCPVyg6HWYZuHYZaLfZ8Giqk1NHJvfMyk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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