How far in advance of "effective date" are VFR sectional charts usually made available? (US)
According to the product catalog website of the FAA, new VFR charts are available approximately 20 days prior to their effective date. Since 25th of February 2021, the FAA releases new VFR charts every 56 days, aligned with the AIRAC cycle.

The products mentioned in this catalog are posted at Digital Products
approxiamately 20 days prior to their cycle effective dates. They are
also available through FAA Approved Print Providers.