SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '15e75a0bf2cccd6da92f63ed05b08fade28eef4a0832f88b84be02db34664be8' 
  AND token = 'udOqjxakrPSiXvwM16QxSyWkyyE+ACgsBwVBr0TNy/A=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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