Oven – Why do the pre-cooked hams always take way longer than they should

Especially with a fan oven, opening the door can let a lot of heat out, so checking repeatedly can slow things down further. I assume you didn't test the meat with the door still open, that would make things much worse.

When you do check (at nearly the cooking time) anything tightly packed into the container like the skewers in your picture should probably be rearranged, so that those in the middle end up on the outside.

If you put a foil dish on a baking sheet to make it easier to lift out, preheating the baking sheet might help, especially if it starts quite cold. It can also take a while for an oven to come back up to temperature after adding something like frozen chips.

I also suspect that the middle of the inner skewers may have been very cold still, maybe even icy. I know defrosting in our utility room (not directly heated, probably around 12C in what passes for winter here) can take longer than you think. (BTW defrosting at the back of a fridge or in the meat drawer can take a very long time). This wouldn't be enough to explain the whole delay in cooking. As has been noted in comments, defrosting for hours at room temperature isn't recommended by some guidelines, but I and many others wouldn't think twice about it when the room is cool and the container closed.

I suggest that in this specific case a few factors combined to slow things down: the oven a touch under, the food colder than expected, and a lot of heat let out of both the oven and the food with repeated testing.

I would attack it in the following manner:

1. put the ham in the preheated oven, center rack
2. gather the ingredients for your pineapple glaze
3. set the table/buffet/beverage areas
4. prep your salad, cover it with wrap, refrigerate (note: dressing on the side, so the salad won't wilt)
5. prep the wedges and veggies
6. remove ham, and set oven to 400F
7. glaze and decorate (you can use whole cloves to "pin" the pineapple in place)
8. return ham to oven
9. arrange wedges and veggies on the cookie sheets, oiled and seasoned
10. remove ham, set temp to 425F, tent with foil so it retains some of the heat
11. place wedges in oven, set timer for 12 min
12. transfer ham to serving platter
13. place veggies in oven when timer goes off, set timer for 15 min
14. ask guests if they need a beverage refill
15. remove cookie sheets and place wedges and veggies in serving dishes, don't forget to turn off the oven
16. place all food items in the serving area (table/buffet/etc)
17. announce dinner inviting guests to table or buffet, say grace if customary, make a toast if you are serving alcohol, etc.

You can eliminate a lot of stress if you set up your dishes (empty) on the table or buffet tonight (or early in the day). I will even go as far as putting little sticky notes to remind myself which dish goes where. This allows me to make sure that everything is going to fit. But it also allows me to set out the serving cutlery, make sure that the pieces do not need a last minute scrub or polish, and to note whether I have managed to forget something.

Don't worry, a Ham is one of the all time easiest things to make!

note: I added a couple of minutes to allow for heat loss while opening and closing the oven door.