Timed intercourse ruining everything

I sometimes feel like I'm the only one in here who is doing meds with timed intercourse, but just in case, I'm throwing this out there. I also don't mean to complain, I am just so frustrated!
I feel like timed intercourse is ruining everything. Tonight, for example, we needed to BD and we've known this for a couple days. I had a long, hard, taxing 12 hour shift and the last thing I wanted to do tonight was BD but I was trying to make the best of it. However, neither one of us could really get in the mood and after trying several different things for nearly 45 mins, we just gave up. Now I have to wake up who knows how early before my 12 hour shift tomorrow because we have to BD before the 72 hour window is up.
I am beginning to think this is never going to happen for us. We have schedules that don't make BDing easy timing wise and jobs that are taxing emotionally and physically, so some days, we really just need to unwind and come down from our days before we go back the next day. We have tried all sorts of things to spice it up (and most of the time it's great) but sometimes it just isn't a good time and it isn't going to happen.
Any of you ladies doing timed intercourse (or who have): how do you make it happen when it just isn't working?