To speed this up, you can create a custom castle with only one room, right by the gate. I used the Golem room (Kingdom), as it's a large target with thin walls.
The best thing about this is you can actually blow up the room *yourself*, by firing an explosive apple at your own gate. Total time is 20 seconds per level (plus menus).
Additional notes:
1. The achievement only counts "Survival" - you don't need to play "Hero Survival".
2. You need to play the first eight missions. The achievement unlocks as soon as you lose the eighth one.
3. You do actually need to set a positive time for each level. You can't just use a castle that falls down by itself.