This is a English version of #2.
If you can understand words in #2, you can just skip.
In v1.5, "Time-limited Challenge" mode was added.
The rule is easy. You should accomplish as many waves as you can in 20 minutes.
Then, which time is limited?
In fact, the 20 minutes only includes card-choosing stage, planting stage in elite level, and time spent in defeating Zombies.
Time spent in loading the level is not limited.
Pause can stop timing.
It can be seen that this kind of time is similar to game time in speed run.
However, game will not end instantly when you use up your time in card-choosing stage or planting stage, until zombies begin their attack.