Jetson Nano will forget date and time when powered off if you do not have RTC backup power supply (such as a battery or a supercapacitor). If the clock was reset after powering off, when you turn it on and there is no Ethernet or WiFi connection, it cannot know current date and time.
I solved this by adding small supercapacitor for the RTC so it can keep correct date and time even when Jetson Nano is turned off (I also had to increase charging current and voltage for the supercapacitor, this is how I did this in case somebody is interested: Is it possible to increase RTC supercapacitor charging current? - #5 by Lissanro). Adding a battery for the RTC is another option: https://custom-build-robots.com/top-story-en/nvidia-jetson-nano-real-time-clock-rtc-part-1/12774?lang=en.