Just to throw my twopenneth in (I'm afraid you're too far away for me to join you, although you never know come summer). To start at 7am and finish at 2pm, you will be fairly motoring. As an example, I did 125 miles yesterday leaving home at 6.30am, joining Ianrauk at 7.30am. I got home at 3.45pm and neither me nor Ian are what could be described as slowcoaches over this kind of distance.
Personally, and I won't be offended at all if you completely ignore me, I'd set a target return of 4pm from say a 7.30am start. This adds a bit of enjoyment to the ride rather than turning it into a game of attrition particularly if you run into an unexpected headwind or something. You may still get back at 2pm which would then be a bonus rather than returning at 3.30pm and missing your target. (I told SWMBO I'd be home around 3 yesterday, got a text at 3.15 to ask where I was!!! I count 3.45 as around 3!!)