I didn't come across any reference to this (might have missed it)...
originally, a number of versions ago, I was able to set up devices with a "manual" refresh frequency.
Refresh Frequency
The refresh frequency controls how often you would like to have the data updated. It is recommended that you set this value to the longest useful time. Some data sources may only need to be updated once per day.
I made some changes to a few of my devices recently and now "manual" refresh appears not to work, I have to set an actual time from the drop down list.
Thanx in advance for you help.
Dave