Timers in Singular overlays are all built using the Timer Widget which operates off of Coordinated Universal Time (UTC). If you're seeing different times on different devices in your production pipeline (for example the operator computer and a rendering computer) one or multiple devices might need to be synchronized to "internet time".
How to synchronize to "internet time" for Windows 10 >> https://www.groovypost.com/howto/synchronize-clock-windows-10-with-internet-atomic-time/
How to synchronize to "internet time" for Mac >>
Windows OBS users, if this didn't help resolve the issue, your version of OBS could be the problem. Update OBS to the latest version by selecting Help > Check for Updates.