Hey Johnston,
Upgrade times vary depending on the number of dSources and VDBs that you have. Normally we recommend planning for 1-2 hours of downtime however it could be much shorter.
In terms of upgrading yourself, currently this is done with the help of support, we encourage our customers to stay up to date and aid them in upgrading whenever they choose. Upgrading is a fairly simple process and support likes to be in on this process because we like to run a validation of your Delphix Engine before we upgrade you.