Actually M700 and M300 do not support the settings_refresh_timer option so it won't do periodic configuration requests as Desktop Phones do. I think this feature is fundamental to manage remotely M300 and M700 so I hope you can implement it in the near future.
Why is this not implemented?
There is a feature request for this with reference ID DECT-354. As soon as the feature is added you should be able to see this ID in the release notes.
As alternative you can periodically send a SIP NOTIFY to the phone with the check-sync header, which will re-trigger the configuration request. The header should look like this: