A1: Beagle Bone Green works in the temperature range of 0-75 Deg Celsius.
Q2: Are there any instructions for using the Grove RTC with the Beaglebone Green on the Debian image?
A2: Grove - RTC needs 5v Vcc but BBG operates only at 3.3V. So they are not fully compatible. But there are still some ways to make them work.
Method One: Pull out the Vcc(Red) wire from Grove - RTC and then plug it to P9_5(5V) on BBG. The connection photo is as below.
Method Two: Use one Grove Cape for Beaglebone Black, which includes 5/3.3V volt converters.
Please find the BBG compatible groves in the following link.
Q3: Does the BeagleBone Green still have a RTC?
A3: The RTC has been removed in the new version of BeagleBone Green. A Grove RTC can be used instead with the method above.