Sorry I don't have measurements but I just got a Selle Italia SLR Lady Gel FLow (different from the Diva Gel Flow and from the Lady Gel Flow - it's pretty confusing, they have millions on their web site). The cutout is HUGE, which comes with its own problems, but maybe for the TT position it would help. It is a t-shaped saddle, compared to the pear-shaped Lady Gel Flow. Longer nose, more drastic drop between the nose and the sitting area.

If the "scene" is friendly around you, aren't there bike shops that would allow you to try the saddle for a week and bring it back if it doesn't work out? It's pretty common practice here. The saddle just has to be "like new" so obviously you can't ride the hell out of it but it gives you enough time to have at least a tentative "yay" or a definitive "nay."

Perhaps tilting the saddle nose a tiny bit (and I really mean tiny bit) would help? My first day on the SLR Lady Gel Flow was a comedy of pain, and then I dialed the angle just right and I'm a happy camper.

Good luck. I understand that saddles for TT can be a big issue... especially over such long distances!

Enjoy your return to cycling!