The input is distance and time.
I'm wondering why time. After all distance is all you need and the device does its job for the set distance.
A delay would be nice tough.
Like 5km, 4 hours.
Just hide it at night and safely escape the island.

So to me it feels like distance/time is the expansion speed. In our case Ibara set 2000m 15 minutes, so 8km/h or roughly 5mph
Which is easy to escape at a slow running pace. I guess Senku had confirmation with the others lining up at fixed intervals.

But the most important thing happening is suika getting petrified. That means she won't need glasses anymore and become the most beautiful loli ever once depetrified. I guess Moz will side the science kingdom when that happens....