It was crucial to be on the field as late as possible, however crappy pollster one could be.
Selzer should've done the 27th-30th rather than the 26th-29th. And even maybe go into the field on the 31st and done revisions if necessary.
Selzer polls for a newspaper. A newspaper's most lucrative edition of the week is the Sunday edition, and newspaper pollsters tend to release their polls for that edition. All polling needs to be done before Saturday in order for the relevant articles to get into Sunday's edition.