According to https://support.aternos.org/hc…0026950972-Stop-countdown ,the server countdown when there is 0/20 players says the countdown is 5/3 minutes. This is no longer true, and it is 90 seconds. 90 seconds is very short, especially when you use a complicated non-vanilla client that takes 3 minutes to start. I remember a month ago when the countdown was 9:15-ish when the server starts and 5-ish when the last person leaves. This would be enough time if the non-vanilla client's servers were overloaded by a huge player spike like the novel Coronavirus. Unfortunately, the opposite happened and my server has to wait in unusually long queues twice.
Conclusion
I completely understand the issue with aternos's ad revenue and limited resources. I can tell that on Friday Aternos has seemed to implement a very powerful afk-player kicker that kicks afk players very well. However, making this countdown time short is not the best approach.