Use of onsite septic systems to treat wastewater is projected to increase in upstate NY. Greenhouse gas (GHG) emissions from septic systems are a potential source of pollution that has been quantified by only two studies to date. Neither of these studies considered the temporal variation of trace gas emissions. Here, we seek to refine existing estimates by measuring GHG emissions in seasons other than summer and across a 24‐hour period. Over the June to December sampling season, N₂O emissions were significantly greater from the leach field than the control lawn between June and mid-August; all other gas emissions were comparable to the control lawn emissions throughout the study. In the course of one 24‐hour period in early August, N₂O emissions were significantly higher from the leach field than the control at 15:00; CH₄ emissions were significantly higher from the leach field at 22:00. These results indicate that septic system GHG emission measurements must be considered in context of time of year and time of day, and scaled appropriately.