You don’t need to report that often and wastes bandwidth. In fact I set plotwatt to only oust every 12 updates from the device.the meter logs total usage and that is what you are reporting and logging so it will be the same in the end if you report every 5 minutes or every 3 hours.
Wastes bandwidth? Is there a shortage of bytes? Seriously, it’s 4 http posts per min - about 100 bytes each. Loading this single forum page uses as much bandwidth (I measured) as 50,000 pushed meter readings.
Also - you DO need to send more than 1 sample per min if you want plotwatt to do the appliance/source ID and per-source cost estimation. I realize that the total in the end is the same… but if all I wanted was the total in the end I could just look at my electric bill every month. The whole point is to get the fine-grained feedback to gain insight into specific energy patterns and consumption of my house.
In peak-time there is indeed a shortage of bytes. Every sunset and sunrise is a crap-shoot whether a scheduled event will execute.
You can batch your samples to reduce load in transporting and to reduce load at Plotwatt.com in processing - and you can STILL get whatever high frequency samples you choose. Until Plotwatt gives up on free service anyway - just a matter of time and volume.
I doubt it’s their internet bandwidth that causes the sunrise/sunset issues… and the fact that the v1 hubs don’t generate the sunrise/set events locally (talk about wasting bandwidth) - I happen to have a v2 hub, so I guess I’m saving bandwidth that way 
And yes, I cache, but since the HEM device type doesn’t run locally, every transaction goes across the interwebs anyway.