No, I'd say Harima not showing up is normal. He's a loner so it wouldn't be unusual for him not to have heard about the walk, or there could easily be something that's causing him to be late. It's Eri's absence that I find strange, since she played a part in setting up this get-together and all her other friends are present. Also, a lack of spoilers for the next chapter seems to suggest that these two aren't going to show up next chapter, either (whether or not we get spoilers nowadays appears to completely hinge on Harima).
Originally Posted by Itchabod
Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you. - Friedrich Nietzsche