ok nevermind, I found this response of @YAP and I also checked the Wiki:
An
Assetis a record consisting of a symbol (for example, “ICP”) and a class (eitherCryptocurrencyorFiatCurrency). The full candid file can be found here. The optional timestamp in the request must be a UNIX timestamp in seconds when provided. If no timestamp is provided, the timestamp corresponding to the start of the current minute is used. Note that the granularity for requests is 1 minute, so seconds in a timestamp are ignored.