This paper aims at differentiating Martin Heidegger’s phenomenological ontology from Emmanuel Levinas’s phenomenological ethics on the experiential level of encountering otherness. In addition to drawing from each author’s seminal texts, I will contextualize the disagreement between Heidegger and Levinas to Irene McMullin’s Time and the Shared World: Heidegger on Social Relations. McMullin, in her response to Jean-Paul Sartre’s criticism of Heidegger’s ontology, provides a formulation of Heideggerian temporality that markedly deviates from Heideggerian ontological commitments in Being and Time. I present and develop two deviations: (a) McMullin positions Dasein’s original encounter with the Other before the establishment of Dasein’s ontological structures (i.e., Being-in-the-world and Being-with-others) and (b) McMullin attributes Dasein’s inauthenticity to the Other’s limitation of Dasein’s temporalization of Being. I contend that both deviations correspond with Levinas’s phenomenology of temporality more than Heidegger’s phenomenology of temporality. It is through McMullin’s deviations, therefore, that distinctions can be drawn between Heidegger’s ontological articulation of Being-guilty, the call of conscience, Being-towards-death, and Angst on one hand and Levinas’s metaphysical articulation of conscience, shame, and death on the other.