SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a8a4648896af3b28b110560bb16a3106e5fa9d9a0161c97972bc8372bc721039' 
  AND token = '4qwIzRbmjxVxZMyuM+ZlV0tEhESRXN2/gslMpAtEd/8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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