<% If #9:00:00 AM# <= Time() AND Time() <= #9:00:00 PM# Then %>
<img src="xyz.jpg">
<% End If %>
*or*
<% If Hour(Time()) >= 9 AND Hour(Time()) <= 21 Then %>
<img src="xyz.jpg">
<% End If %>
*or* (okay, this one is silly, but just to show the weird things you *CAN* do)
<% If ( ( Hour(Time())+15 ) MOD 24 ) <= 12 Then %>
<img src="xyz.jpg">
<% End If %>
Personally, I would keep it simple and go with the first one.