i usually get my letter about 2-3 weeks after i should have received my gear.
if i should my gear on the 1st of a month, then i'd get my letter no later than the 21st-ish.
if you should receive your gear on say a friday, then it should be passing though customs the monday prior. if it gets seized, it's only a question of how long it takes them to process the seizure and send you the notice.
remember, the seizure notice is being mailed domesticly. so it won't take too long.
i keep reading that it can take months to receive a seizure letter. i've never had to wait that long. i think my shit gets processed in chicago, maybe they are really fast with sending the letters out.