Imagine that you are using a wildcard filter '%XXX%' which runs automatically after one second and search across 10K rows datatable with 10+ fields.
From the point of view of infrastructure resources optimization, it seems inefficient to filter a single character because it will send back almost everything in almost any case.
What do you think about the user experience? Does the user expects that the filtering starts with a single character, knowing that most users will probably type 2+ characters anyway? Will it seem strange that the filter does not run when a key is pressed?