LvL 20 complete or reach LvL 20?

[rGghost]

Im right now waiting on a 1200 respawn with 4 guys left with 1 enemy left, on wave 19.

does the achievement unlocks at start of 20 or end?

[GirlPower23]

Just need to reach it.

[rGghost]

I LOVE YOU, YOU SAVED US 400 SEC

[skyg4zer]

Thanks a lot!