Monday evening I went out to run a 5k, dutifully warmed up, and then started my tracking app. I pushed myself but felt slow and was surprised at how difficult the whole effort felt. I was displeased with my finishing time and figured I must have walked more than I thought and been slowed down by the humidity. Not every run can be great, so I let it go.
Today I realized what was going on. I'd left my app settings to measure distance based on a constant speed of 16:40 min/mile (which I use for walking around my office sometimes) instead of GPS tracking and ended up running a 4.25-mile "5k." Counting warm-up and cool down, I did 4.9 miles total.
That would explain why it took me nearly an hour. Good to know. And I'll not make that mistake again.