The guidance says to stagger two hosts' collections, and never says how
long one takes — so an operator picking `dates` has no way to know
whether their stagger is wide enough.
The number that matters is theirs, not mine: a collection's wall clock
is dominated by the sweep over unused `.links` entries, which scales
with the size of the store rather than with what the run deletes. So a
store's size, not its churn, decides the window, and `randomizedDelaySec`
spreads only the start.
Measured here for scale, and deliberately kept out of the doc since it
does not transfer: 11 runs over two weeks ranged 5min 16s to 51min 25s,
inversely — the 51-minute run deleted 732 paths, a 12-minute run deleted
21,901.
Refs #4019.
6d4e0e5fa1