How often/quickly does a Splunk universal forwarder read a file?

Hi, I have some customers who are VERY concerned about the Splunk universal forwarder on their servers. We run tests, and it performed fine, but they are still concerned and would like to know exactly how often/frequent Splunk "wakes up" (their term) to read files. I know that splunkd is always running, but is there some timeframe on how often it checks for new data?