"Ack" is not something done by time period, it's done to acknowledge that a complete chunk of data (frequently " I have received blocks up to block number ##" because TCP can ACK more than one block at a time) has been received.
You can hard set the "window," as a maximum value but it is negotiated at the beginning of the TCP session to the largest value that both sides can agree to.
If there's no ACK, then the "next" block(s) of data will not be sent.
If you need unacknowledged transmission, then you'd usually use UDP instead of TCP.
What is it you're trying to accomplish?