This should be possible without a battery powered RTC
From the development mailgroup
What we have done in v3 (apart from change to switching power supplies) is make sure we have full sleep and power control of each and every peripheral. This means that in software we can selectively sleep/awake and power on/off individual devices as necessary. This is done right down to the individual component chip levels. In full deep sleep, with everything unessential powered down, we can get to about 1mA. The partnership with Hologram should also allow us to put the modems into sleep mode, and use SMS messages (sent via Hologram API from the OVMS server when an App connects) to wake up.
In the moment the sleep modes are not active since the firmware is in beta.
But why don´t you make a request for your feature to the developers on github?
BTW: You can currently set the interval for sending datapackets to the server in idle mode.
(Default IS 60 minutes)
1mA with the main processor in standby should not be that big of a concern, or is it?