Maybe there could also be a maximum amount of time per move that would trigger the warning sign for live games? Like if the total estimated game time is greater than 4 hours or so? (see topic Slow live time setting)
To compute an estimation of the (soft) max total game duration, you could use something like (per player) softMaxTotalTime = basicTime + 120 * increment. And perhaps apply a reduction factor for byoyomi (maybe 0.5?), because in general byoyomi gets partially lost, which doesn’t occur with Fisher increment.
I haven’t figured out yet how to account for Fisher maxTime.