I want to report the number of logins on my system by day. Is there some way to schedule the 24 hour search every day and show a chart of the daily counts so far? I am thinking this is more efficient than searching the daily count over the history of the index.
Have you considered the in July 2016 released Monitoring Splunk Users and Knowledge Objects App ?
It has a nice view with lots of statistics and also a graph of daily users logging in. Turning the search into a weekly (mail) report might be an idea; or implementing the panel into dashboards.