Question about ST100T fan adjustments

I'm installing a "Silent Tornado ST100T" extractor fan. The PCB has two adjustments, one marked "on" and one marked "off". Presumably the "off" adjustment is to set the run-on time, but what's the other one for - switch-on delay perhaps? The documentation doesn't mention it.

Could be. Some fans support a switch on delay, so when being triggered by a light switch, you can prevent them from running for "short" visits to the bathroom.

(I rigged up one with a similar delay at start, run on timer, humidistat control, and also periodic "refresh" airflow (where it runs for a few mins every few hours). SWMBO complained that it seemed to "have a mind of its own". Which indeed it did! (once she understood the parameters she was happy)

I think it's a delay on timer. Is this the one with dip switches on it?

I haven't encountered one with an "on" delay but I can't think what else it could be. There aren't any switches - it's the one that claims to be the quietest on the market (not necessarily the most effective)