With all due respect, I do believe that no self respecting Southerner (especially those who's people are of the Old South) would ever wear seersucker [or white] before Memorial Day unless they are attending an equestrian event or on Easter Sunday.
From
Men.Style.Com "The online home of Details and GQ"
You should wear your seersucker when Memorial Day arrives or when you travel between 23.5 north latitude and 23.5 south latitude.
And from
Soco's Guide to Being a Southerner, vol. 1
Seersucker: You don't wear white before Memorial Day, so you don't wear seersucker, either.