How to install timer on 3-gang switch
Alright, a note on your diagrams -- line and load are purely electrical designations that have no relevance to the mechanical placement of cables in the box.  That said, your box is wired as follows:


"Line 3" is likely the actual circuit coming into the box
"Load" is carrying unswitched power out on both wires (black and red) for some odd reason
"Line 1" goes off to the garage flood light
"Line 2" goes off to the porch light
"Line 4" goes off to the foyer light


Given this, we can determine that your existing plan for installing the timer is incorrect -- the timer's blue load wire needs to go to the black wire coming out of Line 1, while the timer's black line wire needs to go to the junction that feeds all the switches.