@Nullable
    public static String formatHiddenDate(final Geocache cache) {
        final Date hiddenDate = cache.getHiddenDate();
        if (hiddenDate == null) {
            return null;
        }
        final long time = hiddenDate.getTime();
        if (time <= 0) {
            return null;
        }
        String dateString = formatFullDate(time);
        if (cache.isEventCache()) {
            // use today and yesterday strings
            final String verbally = formatDateVerbally(time);
            if (verbally != null) {
                return verbally;
            }
            // otherwise use weekday and normal date
            dateString = DateUtils.formatDateTime(CgeoApplication.getInstance().getBaseContext(), time, DateUtils.FORMAT_SHOW_WEEKDAY) + ", " + dateString;
        }
        // use just normal date
        return dateString;
    }
Formatting of the hidden date of a cache

@return {@code null} or hidden date of the cache (or event date of the cache) in human readable format
main/src/main/java/cgeo/geocaching/utils/Formatter.java