The original could be written as 1x30s + 10x1m byoyomi.
It looks indeed similar to 21x30s byoyomi which I agree is the best approximation.
Well… it’s “automatically handmade” .
A referee takes away a token from a pile.
There are 10 tokens in each player’s pile.
I’m not sure how to translate “on top”.
When 31s arrive without a move, the referee removes one token. Half of that minute is already spent. There are 29s left until the token expires.
Yes, after one token is removed, if the player doesn’t make a move in that time, another token is removed, allowing 60 more seconds and so on.
Regarding that, the 21x30s byoyomi solution is a bit more friendly because the player can spend his extra time with a finer granularity (30s instead of 60s at a time).
Now I wonder what an average OGS user would think about a challenge with that unconventional time setting.