A simple Internet search will turn up a lot of information on this subject. if you add
rfc to your search, you will get links to the RFCs. For instance, RFC 793, TRANSMISSION CONTROL PROTOCOL:
Note that when the receive window is zero no segments should be
acceptable except ACK segments. Thus, it is be possible for a TCP to
maintain a zero receive window while transmitting data and receiving
ACKs. However, even when the receive window is zero, a TCP must
process the RST and URG fields of all incoming segments.
Based on the comments and discussion, the timer is not paused, it continues to run and may expire. If the ACK for the expired timer is received before the window size is reset, the timer is moot since the segment(s) was acknowledged. If the window size is reset before the ACK is received, the timer has already expired since it continued to run, and the sender will immediately resend the unacknowledged segment(s). It will not resume a paused timer and wait for it to expire.