Sometimes, users will have one or more multi-timers started across the organization that have not been completed yet. This method will allow you to find those that are "in progress" timers.

How do I report on my users who have in progress multi-timer entries that have not yet been committed to actual time records?

The best approach is to create a report, grouped by users and/or matters, on the Timer object. Optionally, schedule this report at intervals so you can evaluate whether users need to be reminded to complete outstanding timers using scheduled reports.