Absentee ballots: How long does it take mail to reach overseas destinations?

Factual Questions
1

I’ve never sent snail mail outside of the US, otherwise I might have a clue.

What with all of this alleged voter disenfranchisement business being bandied about, I wonder how long it really takes to get mail to US citizens abroad. For purposes of working this into the election fiasco current events, I guess I’m thinking mainly about absentee ballots- do they have some kind of special high speed priority? Doesn’t mail destined to military personnel zoom over on USAF jets, reaching its destination in a day or two?

Mail travelling inside the US seems to be hit-or-miss sometimes, so I have to believe that we need to be extra-generous when allowing overseas US citizens time to receive their ballots. For example, if it takes a week for a ballot to get to (say) Afghanistan, we should allow at least two weeks.

Are there any laws that say by what date absentee ballots must be mailed?

2

I am relatively sure that it depends on the state in which you are voting.

Last time I checked, in my state (WA), they needed only to be postmarked by election day. (Which is, IIRC, one reason that it took so long to count the ballots in 2000 - they needed to wait for them all to come in)