even when the next departure is outside the window (i.e., arrive 1 AM and depart 6 AM), I've generally found that the website will not price it out as a thru fare, so you will probably need to call Web Support

<dig> once again, IT doing what it's been told to do ... "IF domestic connection time >4 hours or IF international connection time >24 hours THEN $fare=$leg1+$leg2" ... rather than what you may want it to do </dig>