Like clockwork 3 pm is the time of day that I receive the most amount of cancellations by FAR!
It is the worst time of day in terms of our energy level and it's usually when we can't wait for 5 pm to hit so we can head home and veg out. When I was working in the corporate world I did two things to combat this 3 pm problem:
First, I ran home from work. I got home faster than I would have with the TTC and I was able to kill two birds with one stone. You will get used to running with a backpack and it's such a nice feeling to get outside after a long day trapped inside. The second thing I did that really worked was I told myself I wasn't allowed to think about my workout at all during the day. The more you think about working out the less likely you are to actually do it! I had to just go on auto-pilot mode and get to the gym and then decide.
I'm convinced the hardest part of any workout is just getting your shoes on and out the door. Once you're there I've found I often surprise myself even on days I feel like bahhhhh. When I'm there I give myself 12 minutes. If I'm still hating life after that time I'm allowed to quit and walk away from the workout with no feeling of guilt at all. I've used the 12 minute rule about three times in my life but it's made me go to 100s of workouts I wouldn't have gone to otherwise.
Don't fall for the 3 pm slump! Take 3 deep big breaths, go have some water and stop thinking about working out and just do it instead, you'll always feel much better after it's done. Even if your workout is only 20 minutes long you can make it count! Take that 3 pm!