@Override
        void apply(DateTimeParserContext ctx) {
            int sign = 1;
            if (ctx.isSymbolAtCursor(DateTimeTokenizer.Symbol.MINUS)) {
                ctx.cursor().inc();
                sign = -1;
            }

            // FIXME: handle overflow
            long timestamp = ctx.readLongAtCursor() * sign;
            ctx.setUnixTimestamp(timestamp).cursor().inc();
        }
The base time for relative statements.
exts/jphp-zend-ext/src/main/java/org/develnext/jphp/zend/ext/standard/date/DateTimeParser.java