I don't think you have to have a conversation about this with her.

I think YOU need to have a plan.

Just because she "makes herself available" or "initiates" does NOT mean you have to take her up on it.

You need a plan for those times, to be direct IN THE MOMENT.

"Wife, I would love to be with you, but it will take about 15 minutes for pill to take effect. I dont' have that kind of time this morning, but I am certainly looking forward to our SCHEDULED time to be together tomorrow". Or something along those lines.

Don't talk to her about it--it only adds pressure to her, and depression to YOU.

She did a good thing by offering (though I suspect she knew she had spin class the next day, and wanted an out). Doesn't let her OUT of the next day's planned session. And if you address it in teh moment, you will both feel more manly, and you will increase your chance of getting what you want.

No more "wah wah wah, this doesn't work for me" talk... (in my opinion). SHe doesn't care!!!! BE direct and honest (radically so) IN THE MOMENT.