Copilot agent returns incorrect dates in outputs
Veronique's Blog reports that Microsoft Copilot agents can return incorrect dates and times, sometimes interpreting day-month values as month-day or producing apparently random future dates. The author says the problem can appear suddenly without configuration changes and warns it "could have serious consequences" depending on downstream processes. Veronique documents a checklist of settings to inspect, including Microsoft 365 profile language and regional format, Outlook calendar time zone, tenant and Power Platform user settings, agent language in the Copilot "Agent settings", browser language, and local computer time and region. The post attributes improved results in one case to turning Allow ungrounded responses off and describes a mitigation using Power Automate with the Convert time zone action and adjustments to the Conversation.LocalTimeZone system variable.
What happened
Veronique's Blog reports that a Microsoft Copilot agent returned incorrect dates and times, at times treating UK-format dates like 07/05/2026 as the US-format 5th of July 2026 or producing apparently random future dates. The post states the issue can appear suddenly without any deliberate configuration change and warns it "could have serious consequences" for dependent processes. The author says attempts to force a specific format in prompts did not resolve the issue in her case. The blog notes the agent in the reported example had both Knowledge settings enabled and that disabling Allow ungrounded responses produced a better output.
Technical details
Editorial analysis - technical context: Date-time handling is a recurring integration pain point across web platforms, calendar systems, and localization layers. Differences between en-GB (day-month-year) and en-US (month-day-year) representations, client locale, tenant-level settings, and agent runtime variables can all contribute to ambiguous parsing. Agents that combine knowledge sources or perform freeform generation may emit ungrounded or reformatted timestamps when internal locale signals conflict.
Solution and workaround
The blog suggests a troubleshooting checklist: verify Microsoft 365 profile display language, regional format, and time zone; check Outlook calendar time zone; inspect Power Platform and tenant user settings; confirm agent language in Copilot "Agent settings"; and check browser and OS time/region. Veronique reports mitigation by disabling and by routing outputs through using the action. The post also mentions adjusting the system variable for more complex scenarios.
