Background: Early advance care planning (ACP) in oncology increases goal-concordant care. However, time pressures during a busy clinic day may prevent clinicians from engaging in necessary conversations. Given prior evidence of suboptimal clinician decision-making in non-oncology settings in latter parts of a clinic day, we investigated the association between appointment time and likelihood of ACP conversations. Methods: We used electronic health record data to identify medical oncology encounters. We ascertained the presence of ACP from either (1) a specific ACP note type in the EHR, or (2) an ACP smart phrase in clinical progress notes. ACP documentation was used as a surrogate for ACP discussions, as ACP documentation is a quality metric used by organizations including the ASCO’s Quality Oncology Practice Initiative. Appointment times between 8am and 4pm were separated by the hour. Oncology clinicians usually practiced in a morning (8am to 11am) or afternoon (12pm to 4pm) session. Time was indicated by grouping appointment times in the order they occur in a session. We used generalized estimating equations, clustering by clinician, to estimate the probability of ACP documentation. Session hour (1-5) was included as a categorical and continuous variable. We adjusted for patient clinical and demographic features. We also performed a sensitivity analysis using a restricted sample that excluded encounters from 12pm. Results: Adjusted odds ratios (ORs) for ACP documentation rates were significantly lower for all hours of a session after the earliest hour (Table), with consistent results in the sensitivity analysis. Conclusions: Oncology clinicians’ likelihood of having advance care planning conversations decreases as a clinic session progresses. Decision fatigue and falling behind schedule could be contributing reasons for this effect. Lower rates of discussions about goals of care later in a session could result in more aggressive end-of-life treatments. Proactive scheduling of high-risk patients earlier in a clinic session or scheduling separate visits for advance care planning could facilitate necessary conversations and should be further studied.