hope this ac power loss detector can help in their future iterations.
the pnp transistor can be any small signal types. I see they use the 2N5401, that should work well. AC1/AC2 is tapped at the main transformer's secondary directly. when power is turned off, C6 (100uf cap at the junction of R10/R11) is immediately discharged to ground through D3, R3 and T1.
now, if you don't want to mess too much with the stock board (I know I wouldn't), another way to increase your turn off speed is as I mentioned above to reduce C5 to about 47uf, then parallel a diode (1N4148 or 1N4007 will do, or whatever is laying around) with R10. this will provide a discharge path for C6 (the turn-on delay capacitor) during turn off and will tremendously improve the cut off time of the relay.