If you own a device that got updated to Android 6.0, you might have noticed something strange about the system clock on your phone. Many complaints have been filed in the Google Code site about the clock running slow after updating to the Android 6.0. This can make the alarms and event reminders set from your calendar absolutely useless.
We're not discussing about a 30 second difference, or even five minutes. As per Nexus users posting on the Issue Tracker (Issue # 189789), the time mismatch can go up to 30 minutes. Some have managed to fix the issue by turning on Airplane mode and then reverting to normal mode again. But this solution won't apply to all the devices.
Rebooting the smartphone is a fix that has resolved the issue for many, but others have reported that switching to a 3G network setting from 4G will get the phone's clock synced with the network.
Updating to Android 6.0.1, will fix the system clock and you won't be late for work anymore or miss appointments. So the modus operandi is to keep trying one of the workarounds until Android 6.0.1 is pushed to your device.