Well done, Jack. It sound like you have confirmed the method on PS2. I figured it would work but couldn't be sure.
In order to reduced your progress to attempt to get the girls to 45% when you collect the last oyster I suggest meeting the girls and remaining in the circle. During my tests I found that the date failed so quickly that the 7 second delay prevented the jealously script from kicking in so the two-timing dates didn't get disabled.
MC_320, you came into this discussion early and I think the old theories have confused things for you. So far my new theory on two-timing dates has been very reliable. Forget everything about reducing progress and collecting oysters. As far as I can tell they have absolutely nothing to do with two timing dates. Review the One-Time Two-Time theory post and see if it works as well for you.
With that in mind, you would have two options for two-timing dates. 1) Start a new game and take the proper precautions to avoid activities that disable the two-timing dates. 2) Use a cheat device program to edit the global variable that has disabled the jealous girlfriends on you favorite saves. It's been a while since I've messed with the global variables on PS2, but I'll see if I can work something up for you.
Cheat Device Codes (untested)
RAW PAL (v1)
Gameshark (GS2v3-4) I think; I've never tried using MaxConvert for Gameshark codes.
NTSCv2 (Greatest Hits)
Note that on NTSCv2 the global variable is for disabling two-timing dates is $1240.
Usage: IIRC, cheat device programs will continually write their values. This will prevent the two-timing dates from functioning properly. The control variable needs to progress through different values depending on the current status of the two-timing date. To use these codes properly it would be necessary to Joker the cheat so it only runs when a certain button combination is pressed, or enable the cheat, load the save, save, quit and start again without the cheat running.
Or, perhaps a conditional check will work better. The idea is to only set the variable to 0 if it is set to -1. Something like this for RAW NTSCv2:
Edited by OrionSR, 30 September 2009 - 07:14 AM.