AVR Freaks

I am using this TM1637 library, the scrolling character is moving too fast. Basically cannot see the scrolling movement for long text message. 

The original CPP code is below.  Can someone advice how to admend this code to make it scrolling in human viewable format for long text message.  

void TM1637::scrollChars(const char *value) {
	uint32_t offset = 0;
	if (value == 0 || *value == 0)
	return;

	while (1) {
		for (uint8_t i = 0; i != TM1637_DIGITS; ++i) {
			const char *p = value + offset;
			setChar(i, p[i]);

			if (!p[i + 1]) {
				_delay_ms(500);//original is 250
				return;
			}
		}

		++offset;
		_delay_ms(500);//original is 250
	}
}