Synchrony, or the timing of information as it is exchanged between participants, has garnered increasing study in online learning. Within this domain is bichronous online learning (BOL), the blending of asynchronous and synchronous elements within one learning environment. Some research has identified mobile instant messaging as quasi-synchronous (able to be both synchronous and asynchronous), but this affordance has been largely unexamined. This study addressed the above gaps by comparing online learning across asynchronous, synchronous, and quasi-synchronous modalities. It was framed by online learner engagement (OLE) which considers affective, behavioral, and cognitive dimensions and various environmental affordances including synchrony. This convergent mixed-method study explored engagement across forums, video chats, and mobile instant messaging (MIM) via qualitative content analysis, text mining, descriptive statistics, and social network analysis. There were several findings: The time students had to prepare their responses before interacting related to all three dimensions of engagement. Affectively, the quasi-synchronous modality appeared the most positive and least negative. Behaviorally, the quasi-synchronous and asynchronous modalities were more like one another than to the synchronous modality. Logistical flexibility afforded by the asynchronous and quasi-synchronous modalities impacted behavioral engagement. The quasi-synchronous debate had a unique dialectical structure compared to the other two modalities. Some students made use of other features within the Zoom debate to create a quasi-synchronous experience toward better cognitive engagement. Although not directly connected to synchrony, navigability seemed related to all dimensions of OLE as well. Finally, evidence among the preceding findings support the proposition that MIM's quasi-synchronicity supports BOL.