We generally tour Epcot in one day. With the tiered FP+ in Epcot, the smartest thing to do is to head to either Soarin' or Test Track at rope drop, and have a FP+ made for the other at least a couple of hours later (or whenever you think you'll have worked your way to the opposite side of Future World). For my family, it takes about 90 minutes to cover the Test Track side of Future World if we start there at rope drop (skipping Ellen's Energy Adventure, and spending only about 10 minutes in Innoventions), and closer to 3 hours to cover the Soarin' side of Future World if we start there at rope drop (skipping the Lion King film and sometimes Captain EO, but lingering for a few minutes at the aquarium exhibits in The Seas and the Imagination play area), so if I wanted a FP+ for Test Track, I'd make it around noon, and if I wanted one for Soarin', I'd make it for around 10:30am. Don't waste a FP+ by making one within the first hour after the park opens: during that hour, the lines are the lowest they'll be all day, and you're unlikely to save any time by using a FP+ then. Save them for later, as the crowds build...
Typically, we then have lunch and head back to the hotel for a nap break. Around 4pm, we return to do World Showcase (including Gran Fiesta boat tour, Maelstrom, and 1 or 2 of the 3 movies offered in China, Canada and France). In your case, you'll likely want to start with the Mexico side and work your way around so you'll be in the neighborhood of Great Britain when your dinner reservation rolls around. As far as other FP+ in Epcot, we generally make them for SSE (late afternoon, as we return to the park, although we generally hit it again on our way out at the end of the night) and then some other random thing.