Prompt answers to messages say to readers that the writer cares about them.  Conversely, late messages tell the reader that the writer is indifferent to the needs of the readers or that the writer is grossly inefficient.

The basic promptness rule is:

• Reply to the email on the same day as receipt
• Reply to memorandum within one day
• Reply to letters within three to five days
• Respond to reports within the timeline established by the cover letter or memorandum