flexfax: How to activate inbound fax during special hours?

[Ali Reza Naddaf <naddaf@math.lsa.umich.edu>]

Hi everyone. I just installed HylaFax4.0 on my Linux box (red hat). I only
have one phone line and I like to use it as a normal phone line (manual
voice answer) during the day (i.e. I don't want HylaFax to answer the
incoming calls) and I want to "turn hylafax on" during nights
for receiving faxes. What's the appropriate setup? 
Many thanks, Ali.