Choose between Bluetooth Low Energy advertizing and connection for low-power small-data application
If you data will fit into an advertising packet payload, then that is the lowest power possible way to get that data delivered to a receiver (or receivers). To send an atomic data set via advertising, you only need to send a single packet. A connection at very least would require a send followed by a receive. 

You also indicate that you could go hours between data packets. With advertising, you can send your packets spontaneously as you like- as long as the receiver gets the packet when you do send it then the transfer is good. 

Advertising packets are also much simpler to create. You could save processor cycles by laying out all the static parts of the packet in memory one and then very quickly updating only the dynamic data fields before a send.