Looks like Alan Lovejoy has posted a pretty comprehensive Date/Time/Timezone library for VisualWorks. The installation page says:

Chronos is currently available only for VisualWorks Smalltalk. The version currently distributed should be compatibile with all versions VisualWorks from 2.0 forward. However, the “file-out” format is NOT compatible with versions of VisualWorks prior to 5i.3.

For instructions and advice for installing Chronos in versions of VisualWorks prior to 5i.3, or for information on porting Chronos to non-VisualWorks environments, see the Porting.rtf (or Porting.html) document that should accompany this document.

The latest version of the Chronos distribution—including all associated documentation—is available from the Chronos website (chronos-st.org.)

Looks pretty useful if you need to deal with calendar/timezone information