SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21e93b09501dffc405b4235765777e596cf59e171310bcdcf357ee6800abab33' 
  AND token = 'UKYVnCX5rthvOZf7UL/6RGZWNKzmkLdZUdGJFmChNlg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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