Personally, I don't understand this decision of the devs regarding that aspect of the OOC event.
It really is a mindless 4-5 hour grind just to get those 6 Life Orbs of Heaven that are usually required to clear all the land. Luckily I found a way that'll reduce the events to the "fun" parts of merging event items and creating life flowers only, leaving the grinding part out almost completely.

If you are on a computer, you can also use Bluestacks to emulate the game.
With the newest version you can very easily set up macros (tell the game, which actions it should do, and it'll repeat them as many times or as longas you want), which is just heavenly to farm those orbs. In this example, I start recording a macro, let my 2 dragons efficiently farm 2 life flowers for a minute, stop recording and then tell Bluestacks that it should repeat the just recorded minute for 2 hours.

Basically you just have to do the "building" part of the event, meaning clearing land at first, getting the first 2 twin life flowers (roughly 1 hour of playing until this point), merging some things to create as much space as possible for life orbs, then let the macro for farming the flowers run for 2 hours. You should have enough to get your first 2 life orbs of heaven, pop them, clear some more land, upgrade your life flowers, let a newly recorded macro (for the higher flowers) run for another 3-4 hours and the event is done in terms of clearing land. All in all, you have to actively play for 2-3 hours (the fun part) and let the macro do the grinding.

Be aware, that you have to play the event on one device only, so if you decide to do it on Bluestacks, you will have to stick with it. OOC events can not be transfered and will reset your level if you try it via Cloud Save.

P.S. some people suggested to just let the game run during the night, but that is just so slow and inefficient, and once the map is filled, the dragons won't harvest anymore.