Maybe I’ll now go and figure out how to add this to the calendar, but just as a very early FYI:
Date: Tue 30th July
Time: 05:00AM UTC - 05:30 AM UTC (approx. - these operations usually only require a few minutes, but this is the allocated time window)
Impact: Wikidata will go read-only. No edits will be allowed. Reads will not be impacted.
(More for the technically inclined.)