There is a flavor for hold-tap behaviour I'd like to have: "hold-on-large-overlap"

Example: Lets say we have key "&mybehaviour LSHIFT A" and key "&kp S".

I often happen to "roll keys", that is, I will type A down>S down>A up>S up regardless of wanting to type "S" or "as". But there is one difference: If I want to type a capital S, there will be a large overlap (in ms, as well as "in percentage of the time where S is down") that overlaps with the time where A is down. But if I want to type "as" the time where both keys are down will be quite small.

Ideally, there would be a free parameter "overlap-time-ms" and if the overlap is at least that time, then hold behaviour triggers.

I can try to implement that behaviour myself,
can you point me into some direction what I would need to do?