Second Life will be down for updates again on Wednesday 22 August from
9am 8am to 11am SLT (US Pacific). Lots of changes are going in for first stage of the Heterogenous Grid, and some of these changes can't be undertaken in a rolling restart. Not and still have the grid, you know, work for the duration.
This update is completely independent of any viewer versions that may be running around. One does not require the other.[Update: Linden Lab say they need an extra hour, and will be starting at 8am, not 9am]