You can add the sunrise and/or sunset times to each day if you have SunCalc by Brian Savage installed. Use the Variable Editor to set the variable SunCalcPath to the path of the SunCalc application.
The settings for SunCalc (the longitute, latitude, timezone, and hour format) are read from the environment variables as described in the SunCalc documentation. FWCalendar can take into account changes to and from daylight savings time (change the AdjustDST variable if your location doesn't participate in DST time changes).