@sudorandom : I didn't find it documented anywhere, but the upgrade time varies from transaction to transaction
For Ram: the avg time for upgrade is 3 min
For CPU, if its from public to private CPU,the avg time is 7 min and if its from public to public the avg upgrade time is 3 min.
The CCI powers down under a min once upgrade order is placed.
Only after all the upgrade transactions are completed(ram and/or CPU),does the CCI becomes accessible again and the reboot is soft reboot which shouldn't take this much time 
Hope it helps