You might want to set the CC timer to your expected departure time or a bit after, since there is no point in heating the car up early and letting it heat your garage; the LEAF, like most cars, is not well insulated and does not hold heat all that well.
If you set charge priority the car shouldn't turn on the CC system "until 10 segments of the Li-ion battery available charge gauge are illuminated." (Nav manual page 2-10) But the initial heating takes more power than the Level 2 EVSE can supply, so some of the heating will likely come from the battery, until it backs off to just maintain the heat level in the liquid reservoir. So, "charge priority" has to do with making sure you are near an 80% charge before allowing the CC system to function, not with keeping the charge level at 80%.
I would have expected that the car would begin charging again to get back to 80% but it may be that the decline in charge is so small that it isn't enough to trigger the charger to turn back on, especially since your end time was 7:45 AM (and the charge likely finished an hour or two before then). Be aware that the tenth bar on an 80% charge is more like 9.6 to 9.7 bars, so even a slight decrease in overall charge will show up as nine bars displayed, even if the charge is actually 9.4 bars or so. So, don't assume that because the fuel gauge displays nine bars instead of ten it means that you are down one full bar from your desired 80%—not so!
I suggest that you try setting your charge end time to a half hour or so after you plan to leave and set your CC timer to 0 to 10 minutes after you plan to leave; you will likely find that the car warms up plenty by then, although it depends on how cold the car is. (I use fifteen minutes after I plan to leave, albeit with CC timer priority, otherwise the car heats up too much.) And don't worry about the car not being at precisely 80% charge when you leave.
