@StngBo, though the repository that @DJ_Volt referred to is a great foundation, it is focused, as he says, on the Electron which is based on the STM32F205 versus the Boron nRF52840. A key difference is the fact that the nRF52840 does not have a Real Time Clock and instead uses a Real Time Counter. Furthermore, that Real Time Counter is not very accurate and does not run during the deepest of sleeps (HIBERNATE).
One way around this issue is to connect to the Particle Cloud on a regular basis to resync the time. Another is to add an external “true” RTC as many have members have done including @rickkas7 (see [here])(https://github.com/rickkas7/MCP79410RK)). He also has a great library for publishing queued data here. @chipmc has also designed a great Gen3 carrier board with the specific intent on providing the most flexible power savings capabilities for remote use.
For once-a-day publishing, disconnecting and turning off the cellular modem probably makes sense. However, what you haven’t mentioned is how often you sample data and store it to the SD. This will impact how you sleep the device and likely a change in the SYSTEM_MODE you are using from AUTOMATIC to SEMI_AUTOMATIC or MANUAL.
You also haven’t mentioned what your power usage targets are. This will also help guide your choices and any advice given by this great Community.