SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a9ef850c250fb925f976e6119243ff23f3303771ceaa66c0670427932f434811' 
  AND token = 'U+zqT+4CTDTV3O0CcWcVfP0cc93I9eOz/3EkpmjYpZE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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