Creates the default produced KeyPackage lifetime: an 84-day range
(7,257,600 s — deliberately ~1h under the 7,261,200 s cap for headroom),
with notBefore backdated ~1h so a peer's minor clock skew does not
reject a just-published KeyPackage as not-yet-valid (D-07).
Returns Lifetime
A lifetime object with notBefore backdated ~1h and notAfter 84 days after notBefore
Creates the default produced KeyPackage lifetime: an 84-day range (7,257,600 s — deliberately ~1h under the 7,261,200 s cap for headroom), with
notBeforebackdated ~1h so a peer's minor clock skew does not reject a just-published KeyPackage as not-yet-valid (D-07).