My charts have 13 September 2018 on them. What time do they expire?
I thought at Midnight that night local time, but have been unable to find any corroborating evidence.
In FAA-land the AIRAC cycle effective time is 0901Z. Your old charts were valid until 13 September 2018, 0900Z, the new ones are valid since 13 September 2018 0901Z.
I can't find the regulation that says it's always the case, but Google FAA 0901Z and you see that will give a ton of new charts / publications.
Here is a Jeppesen publication that explains the interpretation of the effective date.
Unofficial answer is 23:59z if anyone else has the same question. Some FAA personal may or may not allow it till 12:59 Local.
The FAA inspector I spoke with could not provide me documentation on how he came up with that answer.
If you were slapped by the FAA for having expired plates on the day of, they probably were out to get you or your company and you may have a chance to get out of it since it's vague as to to when they really do expire.
Well, legally speaking, in a world where an FAA inspector is waiting to jump out from behind a tree to nail you for an infraction, it would be safe to say 23:59 Zulu on the 13th. But in the practical world, end of the day on the 13th where you live should suffice. In any case, I don't believe there is a regulation in the US that even requires a current chart for VFR flight. So relax.